fix ImagePair MAE comparison (#7477)

Author: pmeier

test/common_utils.py

@@ -292,7 +292,8 @@ def compare(self) -> None:
         actual, expected = self._equalize_attributes(actual, expected)
 
         if self.mae:
-            actual, expected = self._promote_for_comparison(actual, expected)
+            if actual.dtype is torch.uint8:
+                actual, expected = actual.to(torch.int), expected.to(torch.int)
             mae = float(torch.abs(actual - expected).float().mean())
             if mae > self.atol:
                 self._fail(