supress ambiguous reference date string warning (#4590)

Author: mathause

xarray/tests/test_coding_times.py

@@ -86,6 +86,7 @@ def _all_cftime_date_types():
 
 
 @requires_cftime
+@pytest.mark.filterwarnings("ignore:Ambiguous reference date string")
 @pytest.mark.parametrize(["num_dates", "units", "calendar"], _CF_DATETIME_TESTS)
 def test_cf_datetime(num_dates, units, calendar):
     import cftime

xarray/tests/test_conventions.py

@@ -233,6 +233,7 @@ def test_decode_cf_with_drop_variables(self):
         assert_identical(expected, actual)
         assert_identical(expected, actual2)
 
+    @pytest.mark.filterwarnings("ignore:Ambiguous reference date string")
     def test_invalid_time_units_raises_eagerly(self):
         ds = Dataset({"time": ("time", [0, 1], {"units": "foobar since 123"})})
         with raises_regex(ValueError, "unable to decode time"):