BUG: GH39443 - ensure categorical dtype

Author: arredond

pandas/tests/reshape/concat/test_categorical.py

@@ -216,7 +216,11 @@ def test_categorical_datetime_concat(self):
 
         result = pd.concat([df1, df2])
         expected = DataFrame(
-            {"x": Series([datetime(2021, 1, 1), datetime(2021, 1, 2)])}
+            {
+                "x": Series(
+                    [datetime(2021, 1, 1), datetime(2021, 1, 2)], dtype="category"
+                )
+            }
         )
 
         tm.assert_equal(result, expected)