Address code review comment. (#25995)

analysis_options.yaml

@@ -28,7 +28,9 @@ analyzer:
     missing_return: warning
     # allow having TODOs in the code
     todo: ignore
-    #
+    # Ignore analyzer hints for updating pubspecs when using Future or
+    # Stream and not importing dart:async
+    # Please see https://github.com/flutter/flutter/pull/24528 for details.
     sdk_version_async_exported_from_core: ignore
   exclude:
     - 'bin/cache/**'