📝 Update source examples and docs from Python 3.9 to 3.10 (#14900)

docs_src/custom_response/tutorial009b_py310.py

@@ -0,0 +1,10 @@
+from fastapi import FastAPI
+from fastapi.responses import FileResponse
+
+some_file_path = "large-video-file.mp4"
+app = FastAPI()
+
+
+@app.get("/", response_class=FileResponse)
+async def main():
+    return some_file_path