docs: fix inconsistent response code when item already exists

In https://github.com/tiangolo/fastapi/pull/4482, the response status code was changed to return 409 when the item already exists in non-Annotated examples, but left as 400 in the others. Seems like an oversight, unless this was done intentionally for a reason I'm not aware of.

docs_src/app_testing/app_b_an/main.py

@@ -34,6 +34,6 @@ async def create_item(item: Item, x_token: Annotated[str, Header()]):
     if x_token != fake_secret_token:
         raise HTTPException(status_code=400, detail="Invalid X-Token header")
     if item.id in fake_db:
-        raise HTTPException(status_code=400, detail="Item already exists")
+        raise HTTPException(status_code=409, detail="Item already exists")
     fake_db[item.id] = item
     return item

docs_src/app_testing/app_b_an/test_main.py

@@ -61,5 +61,5 @@ def test_create_existing_item():
             "description": "There goes my stealer",
         },
     )
-    assert response.status_code == 400
+    assert response.status_code == 409
     assert response.json() == {"detail": "Item already exists"}

docs_src/app_testing/app_b_an_py310/main.py

@@ -33,6 +33,6 @@ async def create_item(item: Item, x_token: Annotated[str, Header()]):
     if x_token != fake_secret_token:
         raise HTTPException(status_code=400, detail="Invalid X-Token header")
     if item.id in fake_db:
-        raise HTTPException(status_code=400, detail="Item already exists")
+        raise HTTPException(status_code=409, detail="Item already exists")
     fake_db[item.id] = item
     return item

docs_src/app_testing/app_b_an_py310/test_main.py

@@ -61,5 +61,5 @@ def test_create_existing_item():
             "description": "There goes my stealer",
         },
     )
-    assert response.status_code == 400
+    assert response.status_code == 409
     assert response.json() == {"detail": "Item already exists"}

docs_src/app_testing/app_b_an_py39/main.py

@@ -33,6 +33,6 @@ async def create_item(item: Item, x_token: Annotated[str, Header()]):
     if x_token != fake_secret_token:
         raise HTTPException(status_code=400, detail="Invalid X-Token header")
     if item.id in fake_db:
-        raise HTTPException(status_code=400, detail="Item already exists")
+        raise HTTPException(status_code=409, detail="Item already exists")
     fake_db[item.id] = item
     return item

docs_src/app_testing/app_b_an_py39/test_main.py

@@ -61,5 +61,5 @@ def test_create_existing_item():
             "description": "There goes my stealer",
         },
     )
-    assert response.status_code == 400
+    assert response.status_code == 409
     assert response.json() == {"detail": "Item already exists"}