[3.11] gh-113086: Add tests for os.chmod() and os.lchmod() (GH-113087) (GH-113089)

Also make test_copymode_symlink_to_symlink in test_shutil more strict.
(cherry picked from commit b4f2c89118d5a48ce6c495ba931d7f6493422029)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>