Fixes #63144

Summary

Corrects the type annotation and default value for the copy parameter in the astype() docstring to match the actual function signature.

Changes

• Updated copy parameter from bool, default False to bool or lib.NoDefault, default lib.no_default
• Location: pandas/core/generic.py, line ~6508

Before:
copy : bool, default False

After:
copy : bool or lib.NoDefault, default lib.no_default