Simplify test case to avoid discrepancies between Python versions

Author: browniebroke

tests/test_fields.py

@@ -212,7 +212,7 @@ class TestXLSXDateField:
             ("2020-01-01", dt.datetime(2020, 1, 1, 0, 0)),
             ("2020-02-03T13:01", dt.datetime(2020, 2, 3, 13, 1)),
             ("2020-03-04T13:15:30", dt.datetime(2020, 3, 4, 13, 15, 30)),
-            ("2020-10-08T15:18:23.1234Z", dt.datetime(2020, 10, 8, 15, 18, 23, 123400)),
+            ("2020-10-08T15:18:23Z", dt.datetime(2020, 10, 8, 15, 18, 23)),
             # Failed parsing
             ("foo", "foo"),
             (None, None),