Merge branch 'mt/t4129-with-setgid-dir'

Some tests expect that "ls -l" output has either '-' or 'x' for group executable bit, but setgid bit can be inherited from parent directory and make these fields 'S' or 's' instead, causing test failures. * mt/t4129-with-setgid-dir: t4129: don't fail if setgid is set in the test directory