[PipelineTesterMixin] Handle non-image outputs for attn slicing test (#2504)

* [PipelineTesterMixin] Handle non-image outputs for batch/sinle inference test

* style

---------
Co-authored-by: William Berman <WLBberman@gmail.com>

tests/test_pipelines_common.py

@@ -450,7 +450,9 @@ class PipelineTesterMixin:
     def test_attention_slicing_forward_pass(self):
         self._test_attention_slicing_forward_pass()
 
-    def _test_attention_slicing_forward_pass(self, test_max_difference=True, expected_max_diff=1e-3):
+    def _test_attention_slicing_forward_pass(
+        self, test_max_difference=True, test_mean_pixel_difference=True, expected_max_diff=1e-3
+    ):
         if not self.test_attention_slicing:
             return
 
@@ -474,6 +476,7 @@ class PipelineTesterMixin:
             max_diff = np.abs(output_with_slicing - output_without_slicing).max()
             self.assertLess(max_diff, expected_max_diff, "Attention slicing should not affect the inference results")
 
+        if test_mean_pixel_difference:
             assert_mean_pixel_difference(output_with_slicing[0], output_without_slicing[0])
 
     @unittest.skipIf(