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

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

docs_src/response_model/tutorial001_py310.py

@@ -0,0 +1,17 @@
+from fastapi import FastAPI
+from pydantic import BaseModel
+
+app = FastAPI()
+
+
+class Item(BaseModel):
+    name: str
+    description: str | None = None
+    price: float
+    tax: float | None = None
+    tags: list[str] = []
+
+
+@app.post("/items/", response_model=Item)
+async def create_item(item: Item):
+    return item