[gunicorn] Add comment for Any annotation

Author: eugeneliukindev

stubs/gunicorn/gunicorn/debug.pyi

@@ -10,7 +10,12 @@ class Spew:
     show_values: bool
 
     def __init__(self, trace_names: Container[str] | None = None, show_values: bool = True) -> None: ...
-    def __call__(self, frame: FrameType, event: str, arg: Any) -> Self: ...
+    def __call__(
+        self,
+        frame: FrameType,
+        event: str,
+        arg: Any,  # `arg` is not used inside the function, stub is set Any
+    ) -> Self: ...
 
 def spew(trace_names: Container[str] | None = None, show_values: bool = False) -> None: ...
 def unspew() -> None: ...