Remove code examples for Python 3.8 in `extending_openapi`

docs/en/docs/how-to/extending-openapi.md

@@ -43,19 +43,19 @@ For example, let's add <a href="https://github.com/Rebilly/ReDoc/blob/master/doc
 
 First, write all your **FastAPI** application as normally:
 
-{* ../../docs_src/extending_openapi/tutorial001.py hl[1,4,7:9] *}
+{* ../../docs_src/extending_openapi/tutorial001_py39.py hl[1,4,7:9] *}
 
 ### Generate the OpenAPI schema { #generate-the-openapi-schema }
 
 Then, use the same utility function to generate the OpenAPI schema, inside a `custom_openapi()` function:
 
-{* ../../docs_src/extending_openapi/tutorial001.py hl[2,15:21] *}
+{* ../../docs_src/extending_openapi/tutorial001_py39.py hl[2,15:21] *}
 
 ### Modify the OpenAPI schema { #modify-the-openapi-schema }
 
 Now you can add the ReDoc extension, adding a custom `x-logo` to the `info` "object" in the OpenAPI schema:
 
-{* ../../docs_src/extending_openapi/tutorial001.py hl[22:24] *}
+{* ../../docs_src/extending_openapi/tutorial001_py39.py hl[22:24] *}
 
 ### Cache the OpenAPI schema { #cache-the-openapi-schema }
 
@@ -65,13 +65,13 @@ That way, your application won't have to generate the schema every time a user o
 
 It will be generated only once, and then the same cached schema will be used for the next requests.
 
-{* ../../docs_src/extending_openapi/tutorial001.py hl[13:14,25:26] *}
+{* ../../docs_src/extending_openapi/tutorial001_py39.py hl[13:14,25:26] *}
 
 ### Override the method { #override-the-method }
 
 Now you can replace the `.openapi()` method with your new function.
 
-{* ../../docs_src/extending_openapi/tutorial001.py hl[29] *}
+{* ../../docs_src/extending_openapi/tutorial001_py39.py hl[29] *}
 
 ### Check it { #check-it }
 

tests/test_tutorial/test_extending_openapi/test_tutorial001.py

@@ -1,6 +1,6 @@
 from fastapi.testclient import TestClient
 
-from docs_src.extending_openapi.tutorial001 import app
+from docs_src.extending_openapi.tutorial001_py39 import app
 
 client = TestClient(app)