[3.12] gh-113188: Fix shutil.copymode() and shutil.copystat() on Windows (GH-113285)

[3.12] gh-113188: Fix shutil.copymode() and shutil.copystat() on Windows (GH-113285)

Previously they worked differenly if dst is a symbolic link:
they modified the permission bits of dst itself rather than the file
it points to if follow_symlinks is true or src is not a symbolic link,
and did nothing if follow_symlinks is false and src is a symbolic link.