✨ 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/tutorial004_py310.py

@@ -0,0 +1,26 @@
+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: set[str] = set()
+
+
+@app.post("/items/", response_model=Item, summary="Create an item")
+async def create_item(item: Item):
+    """
+    Create an item with all the information:
+
+    - **name**: each item must have a name
+    - **description**: a long description
+    - **price**: required
+    - **tax**: if the item doesn't have tax, you can omit this
+    - **tags**: a set of unique tag strings for this item
+    """
+    return item