added a generic Any for series output

Author: muddi900

pandas-stubs/core/frame.pyi

@@ -999,7 +999,7 @@ class DataFrame(NDFrame, OpsMixin):
     ) -> DataFrame: ...
     def stack(
         self, level: Level | list[Level] = ..., dropna: _bool = ...
-    ) -> DataFrame | Series: ...
+    ) -> DataFrame | Series[Any]: ...
     def explode(self, column: _str | tuple, ignore_index: _bool = ...) -> DataFrame: ...
     def unstack(
         self,