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

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

docs_src/extra_models/tutorial005_py39.py

@@ -0,0 +1,8 @@
+from fastapi import FastAPI
+
+app = FastAPI()
+
+
+@app.get("/keyword-weights/", response_model=dict[str, float])
+async def read_keyword_weights():
+    return {"foo": 2.3, "bar": 3.4}