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

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

docs_src/path_operation_configuration/tutorial003_py39.py

@@ -0,0 +1,24 @@
+from typing import Optional
+
+from fastapi import FastAPI
+from pydantic import BaseModel
+
+app = FastAPI()
+
+
+class Item(BaseModel):
+    name: str
+    description: Optional[str] = None
+    price: float
+    tax: Optional[float] = None
+    tags: set[str] = set()
+
+
+@app.post(
+    "/items/",
+    response_model=Item,
+    summary="Create an item",
+    description="Create an item with all the information, name, description, price, tax and a set of unique tags",
+)
+async def create_item(item: Item):
+    return item