gh-155717: skip TMPDIR writeability test if process user is root (#155891)

Author: picnixz

Lib/test/_test_multiprocessing.py

@@ -6357,6 +6357,7 @@ def test_nested_startmethod(self):
         self.assertSetEqual(set(results), set([2, 1]))
 
     @unittest.skipIf(os.name == "nt", "requires POSIX")
+    @support.requires_non_root_user
     @support.subTests("mode", [
         os.R_OK,  # read-only directory
         os.R_OK | os.X_OK, # read-only directory