Correct AccessTokenAuthMetadataPlugin name

It was never itself a "call credentials" of any sort.

src/python/grpcio/grpc/__init__.py

@@ -1196,7 +1196,7 @@ def access_token_call_credentials(access_token):
     """
     from grpc import _auth  # pylint: disable=cyclic-import
     return _metadata_call_credentials(
-        _auth.AccessTokenCallCredentials(access_token), None)
+        _auth.AccessTokenAuthMetadataPlugin(access_token), None)
 
 
 def composite_call_credentials(*call_credentials):

src/python/grpcio/grpc/_auth.py

@@ -63,7 +63,7 @@ class GoogleCallCredentials(grpc.AuthMetadataPlugin):
         self._pool.shutdown(wait=False)
 
 
-class AccessTokenCallCredentials(grpc.AuthMetadataPlugin):
+class AccessTokenAuthMetadataPlugin(grpc.AuthMetadataPlugin):
     """Metadata wrapper for raw access token credentials."""
 
     def __init__(self, access_token):

src/python/grpcio_tests/tests/tests.json

@@ -22,7 +22,7 @@
   "unit._api_test.ChannelConnectivityTest",
   "unit._api_test.ChannelTest",
   "unit._auth_context_test.AuthContextTest",
-  "unit._auth_test.AccessTokenCallCredentialsTest",
+  "unit._auth_test.AccessTokenAuthMetadataPluginTest",
   "unit._auth_test.GoogleCallCredentialsTest",
   "unit._channel_args_test.ChannelArgsTest",
   "unit._channel_connectivity_test.ChannelConnectivityTest",

src/python/grpcio_tests/tests/unit/_auth_test.py

@@ -61,7 +61,7 @@ class GoogleCallCredentialsTest(unittest.TestCase):
         self.assertTrue(callback_event.wait(1.0))
 
 
-class AccessTokenCallCredentialsTest(unittest.TestCase):
+class AccessTokenAuthMetadataPluginTest(unittest.TestCase):
 
     def test_google_call_credentials_success(self):
         callback_event = threading.Event()
@@ -71,8 +71,8 @@ class AccessTokenCallCredentialsTest(unittest.TestCase):
             self.assertIsNone(error)
             callback_event.set()
 
-        call_creds = _auth.AccessTokenCallCredentials('token')
+        metadata_plugin = _auth.AccessTokenAuthMetadataPlugin('token')
-        call_creds(None, mock_callback)
+        metadata_plugin(None, mock_callback)
         self.assertTrue(callback_event.wait(1.0))