TST: Add test case for categorical index assertion fix

Author: Aniketsy

pandas/_testing/asserters.py

@@ -326,7 +326,8 @@ def _check_types(left, right, obj: str = "Index") -> None:
                 mismatch = left._values != right._values
             except TypeError as e:
                 raise AssertionError(
-                    f"{obj} cannot be compared due to incompatible categorical types.\n{e}"
+                    f"{obj} cannot be compared due to incompatible"
+                    f"categorical types.\n{e}"
                 ) from e
 
             if not isinstance(mismatch, np.ndarray):