do not skip a test

The pure Python implementation actually calls the underlying C
functions so in a sense we may still release the GIL.

Author: picnixz

Lib/test/test_hmac.py

@@ -1136,15 +1136,15 @@ def test_update_exceptions(self):
                 self.assertRaises(TypeError, h.update, msg)
 
 
-@hashlib_helper.requires_hashdigest('sha256')
+@requires_builtin_sha2()
 class PyUpdateTestCase(PyModuleMixin, UpdateTestCaseMixin, unittest.TestCase):
 
     def HMAC(self, key, msg=None):
         return self.hmac.HMAC(key, msg, digestmod='sha256')
 
     @property
     def gil_minsize(self):
-        self.skipTest("GIL is always held")
+        return sha2._GIL_MINSIZE
 
 
 @hashlib_helper.requires_openssl_hashdigest('sha256')