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

docs_src/custom_response/tutorial008_py310.py

@@ -0,0 +1,14 @@
+from fastapi import FastAPI
+from fastapi.responses import StreamingResponse
+
+some_file_path = "large-video-file.mp4"
+app = FastAPI()
+
+
+@app.get("/")
+def main():
+    def iterfile():  # (1)
+        with open(some_file_path, mode="rb") as file_like:  # (2)
+            yield from file_like  # (3)
+
+    return StreamingResponse(iterfile(), media_type="video/mp4")