pythongh-128657: Skip test_get_builtin_constructor when running with --parallel-threads (pythonGH-130018)

The test modifies sys.modules and is not thread-safe.

Author: colesbury

Lib/test/test_hashlib.py

@@ -253,6 +253,7 @@ def test_unknown_hash(self):
     def test_new_upper_to_lower(self):
         self.assertEqual(hashlib.new("SHA256").name, "sha256")
 
+    @support.thread_unsafe("modifies sys.modules")
     def test_get_builtin_constructor(self):
         get_builtin_constructor = getattr(hashlib,
                                           '__get_builtin_constructor')