✨ 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/tutorial009_py39.py

@@ -0,0 +1,8 @@
+from fastapi import FastAPI
+
+app = FastAPI()
+
+
+@app.post("/index-weights/")
+async def create_index_weights(weights: dict[int, float]):
+    return weights