TST: Allow test_dti_constructor_with_non_nano_now_today to be flaky (pandas-dev#57535)

* TST: Allow test_dti_constructor_with_non_nano_now_today to be flaky

* Add GH reference

* Add reason

Author: mroeschke

pandas/tests/indexes/datetimes/test_constructors.py

@@ -1031,23 +1031,28 @@ def test_dti_constructor_with_non_nano_dtype(self, tz):
         result2 = DatetimeIndex(np.array(vals, dtype=object), dtype=dtype)
         tm.assert_index_equal(result2, expected)
 
-    def test_dti_constructor_with_non_nano_now_today(self):
+    def test_dti_constructor_with_non_nano_now_today(self, request):
         # GH#55756
         now = Timestamp.now()
         today = Timestamp.today()
         result = DatetimeIndex(["now", "today"], dtype="M8[s]")
         assert result.dtype == "M8[s]"
 
+        diff0 = result[0] - now.as_unit("s")
+        diff1 = result[1] - today.as_unit("s")
+        assert diff1 >= pd.Timedelta(0), f"The difference is {diff0}"
+        assert diff0 >= pd.Timedelta(0), f"The difference is {diff0}"
+
         # result may not exactly match [now, today] so we'll test it up to a tolerance.
         #  (it *may* match exactly due to rounding)
+        # GH 57535
+        request.applymarker(
+            pytest.mark.xfail(
+                reason="result may not exactly match [now, today]", strict=False
+            )
+        )
         tolerance = pd.Timedelta(seconds=1)
-
-        diff0 = result[0] - now.as_unit("s")
-        assert diff0 >= pd.Timedelta(0), f"The difference is {diff0}"
         assert diff0 < tolerance, f"The difference is {diff0}"
-
-        diff1 = result[1] - today.as_unit("s")
-        assert diff1 >= pd.Timedelta(0), f"The difference is {diff0}"
         assert diff1 < tolerance, f"The difference is {diff0}"
 
     def test_dti_constructor_object_float_matches_float_dtype(self):