Making save_load test slow as it times out

tests/models/vit_mae/test_modeling_tf_vit_mae.py

@@ -328,6 +328,7 @@ class TFViTMAEModelTest(TFModelTesterMixin, unittest.TestCase):
 
     # overwrite from common since TFViTMAEForPretraining has random masking, we need to fix the noise
     # to generate masks during test
+    @slow()
     def test_keras_save_load(self):
         # make mask reproducible
         np.random.seed(2)