GH-118447: Fix FreeBSD test failures. (#119170)

Apparently only macOS requires read permission to call `readlink()` on a
symlink.

Author: barneygale

Lib/test/test_posixpath.py

@@ -663,6 +663,7 @@ def test_realpath_resolve_first(self):
     @os_helper.skip_unless_symlink
     @skip_if_ABSTFN_contains_backslash
     @unittest.skipIf(os.chmod not in os.supports_follow_symlinks, "Can't set symlink permissions")
+    @unittest.skipIf(sys.platform != "darwin", "only macOS requires read permission to readlink()")
     def test_realpath_unreadable_symlink(self):
         try:
             os.symlink(ABSTFN+"1", ABSTFN)