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

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

docs_src/body_nested_models/tutorial007_py39.py

@@ -0,0 +1,32 @@
+from typing import Optional
+
+from fastapi import FastAPI
+from pydantic import BaseModel, HttpUrl
+
+app = FastAPI()
+
+
+class Image(BaseModel):
+    url: HttpUrl
+    name: str
+
+
+class Item(BaseModel):
+    name: str
+    description: Optional[str] = None
+    price: float
+    tax: Optional[float] = None
+    tags: set[str] = set()
+    images: Optional[list[Image]] = None
+
+
+class Offer(BaseModel):
+    name: str
+    description: Optional[str] = None
+    price: float
+    items: list[Item]
+
+
+@app.post("/offers/")
+async def create_offer(offer: Offer):
+    return offer