ENH: Verify clipboard io functions

Author: bashtage

pandas-stubs/io/clipboards.pyi

@@ -1,6 +1,10 @@
 from __future__ import annotations
 
+from typing import Any
+
 from pandas.core.frame import DataFrame
 
-def read_clipboard(sep: str = ..., **kwargs) -> DataFrame: ...
-def to_clipboard(obj, excel: bool = ..., sep=..., **kwargs) -> None: ...
+def read_clipboard(sep: str = ..., **kwargs: Any) -> DataFrame: ...
+def to_clipboard(
+    obj, excel: bool | None = ..., sep: str | None = ..., **kwargs: Any
+) -> None: ...