✨ Add docs and tests for Python 3.9 and Python 3.10 (#3712)

Co-authored-by: Thomas Grainger <tagrain@gmail.com>

docs_src/extra_models/tutorial004_py39.py

@@ -0,0 +1,20 @@
+from fastapi import FastAPI
+from pydantic import BaseModel
+
+app = FastAPI()
+
+
+class Item(BaseModel):
+    name: str
+    description: str
+
+
+items = [
+    {"name": "Foo", "description": "There comes my hero"},
+    {"name": "Red", "description": "It's my aeroplane"},
+]
+
+
+@app.get("/items/", response_model=list[Item])
+async def read_items():
+    return items