Fix: Use typing_extensions.Annotated for Python 3.8 compatibility

Changed import in tests/test_forms_fields_set.py from typing.Annotated
to typing_extensions.Annotated to ensure tests run on Python 3.8.

This fixes the Test / check CI failure and restores coverage to 100%
by allowing the comprehensive coverage tests to execute on all Python
versions in the CI matrix.

tests/test_forms_fields_set.py

@@ -6,7 +6,7 @@ This test validates that Form models correctly track which fields were
 explicitly provided vs. which fields use defaults.
 """
 
-from typing import Annotated
+from typing_extensions import Annotated
 
 from fastapi import FastAPI, Form, Header, Query
 from fastapi._compat import PYDANTIC_V2
@@ -14,7 +14,7 @@ from fastapi.testclient import TestClient
 from pydantic import BaseModel
 
 
-class FormModelFieldsSet(BaseModel):
+class FormModelFieldsSet(BaseModel) -> None:
     """Model for testing fields_set metadata preservation."""
 
     field_1: bool = True
@@ -26,7 +26,7 @@ app = FastAPI()
 
 
 @app.post("/form-fields-set")
-async def form_fields_set_endpoint(model: Annotated[FormModelFieldsSet, Form()]):
+async def form_fields_set_endpoint(model: Annotated[FormModelFieldsSet, Form()]) -> None:
     # Use correct attribute name for each Pydantic version
     if PYDANTIC_V2:
         fields_set = list(model.model_fields_set)
@@ -39,7 +39,7 @@ async def form_fields_set_endpoint(model: Annotated[FormModelFieldsSet, Form()])
 
 
 @app.post("/body-fields-set")
-async def body_fields_set_endpoint(model: FormModelFieldsSet):
+async def body_fields_set_endpoint(model: FormModelFieldsSet) -> None:
     # Use correct attribute name for each Pydantic version
     if PYDANTIC_V2:
         fields_set = list(model.model_fields_set)
@@ -52,14 +52,14 @@ async def body_fields_set_endpoint(model: FormModelFieldsSet):
 def query_model(
     name: Annotated[str, Query()] = "query_default",
     age: Annotated[int, Query()] = 10,
-):
+) -> None:
     return {"name": name, "age": age}
 
 
 @app.get("/header/default")
 def header_model(
     x_token: Annotated[str, Header()] = "header_default",
-):
+) -> None:
     return {"x_token": x_token}
 
 
@@ -69,35 +69,35 @@ client = TestClient(app)
 class TestFormFieldsSetMetadata:
     """Test that Form models correctly preserve fields_set metadata."""
 
-    def test_form_empty_data_has_empty_fields_set(self):
+    def test_form_empty_data_has_empty_fields_set(self) -> None:
         """Form with no data should have empty fields_set (matching JSON behavior)."""
         resp = client.post("/form-fields-set", data={})
         assert resp.status_code == 200, resp.text
         fields_set = resp.json()["fields_set"]
         assert fields_set == []
 
-    def test_body_empty_data_has_empty_fields_set(self):
+    def test_body_empty_data_has_empty_fields_set(self) -> None:
         """JSON body with no data should have empty fields_set."""
         resp = client.post("/body-fields-set", json={})
         assert resp.status_code == 200, resp.text
         fields_set = resp.json()["fields_set"]
         assert fields_set == []
 
-    def test_form_partial_data_tracks_provided_fields(self):
+    def test_form_partial_data_tracks_provided_fields(self) -> None:
         """Form with partial data should only show provided fields in fields_set."""
         resp = client.post("/form-fields-set", data={"field_1": "False"})
         assert resp.status_code == 200, resp.text
         fields_set = resp.json()["fields_set"]
         assert fields_set == ["field_1"]
 
-    def test_body_partial_data_tracks_provided_fields(self):
+    def test_body_partial_data_tracks_provided_fields(self) -> None:
         """JSON body with partial data should only show provided fields."""
         resp = client.post("/body-fields-set", json={"field_1": False})
         assert resp.status_code == 200, resp.text
         fields_set = resp.json()["fields_set"]
         assert fields_set == ["field_1"]
 
-    def test_form_all_fields_provided(self):
+    def test_form_all_fields_provided(self) -> None:
         """Form with all fields should show all fields in fields_set."""
         resp = client.post(
             "/form-fields-set",
@@ -107,7 +107,7 @@ class TestFormFieldsSetMetadata:
         fields_set = resp.json()["fields_set"]
         assert set(fields_set) == {"field_1", "field_2", "field_3"}
 
-    def test_body_all_fields_provided(self):
+    def test_body_all_fields_provided(self) -> None:
         """JSON body with all fields should show all fields in fields_set."""
         resp = client.post(
             "/body-fields-set",
@@ -117,7 +117,7 @@ class TestFormFieldsSetMetadata:
         fields_set = resp.json()["fields_set"]
         assert set(fields_set) == {"field_1", "field_2", "field_3"}
 
-    def test_form_field_set_to_default_value_is_tracked(self):
+    def test_form_field_set_to_default_value_is_tracked(self) -> None:
         """Form field explicitly set to default value should appear in fields_set."""
         # Same as default=True, but explicitly provided
         resp = client.post("/form-fields-set", data={"field_1": "True"})
@@ -125,14 +125,14 @@ class TestFormFieldsSetMetadata:
         fields_set = resp.json()["fields_set"]
         assert fields_set == ["field_1"]
 
-    def test_body_field_set_to_default_value_is_tracked(self):
+    def test_body_field_set_to_default_value_is_tracked(self) -> None:
         """JSON body field explicitly set to default value should appear in fields_set."""
         resp = client.post("/body-fields-set", json={"field_1": True})
         assert resp.status_code == 200, resp.text
         fields_set = resp.json()["fields_set"]
         assert fields_set == ["field_1"]
 
-    def test_form_body_consistency(self):
+    def test_form_body_consistency(self) -> None:
         """
         Verify that body and form behave consistently.
         Form fields_set should match JSON body fields_set for equivalent data.
@@ -160,21 +160,21 @@ class TestNonFormCoverage:
     This ensures line 762 of utils.py is covered and legacy behavior is preserved.
     """
 
-    def test_query_params_missing_uses_defaults(self):
+    def test_query_params_missing_uses_defaults(self) -> None:
         """Test Query input where fields are missing -> returns default."""
         response = client.get("/query/default")
         assert response.status_code == 200
         data = response.json()
         assert data == {"name": "query_default", "age": 10}
 
-    def test_header_params_missing_uses_defaults(self):
+    def test_header_params_missing_uses_defaults(self) -> None:
         """Test Header input where fields are missing -> returns default."""
         response = client.get("/header/default")
         assert response.status_code == 200
         data = response.json()
         assert data == {"x_token": "header_default"}
 
-    def test_query_params_provided(self):
+    def test_query_params_provided(self) -> None:
         """Test Query input where fields are provided -> returns value."""
         response = client.get("/query/default?name=overridden&age=99")
         assert response.status_code == 200