Backport PR #31411: COMPAT: dont pass dtype to datetime64 (#31421)

Co-authored-by: jbrockmendel <jbrockmendel@gmail.com>

Author: meeseeksmachine

pandas/tests/scalar/timedelta/test_arithmetic.py

@@ -498,7 +498,7 @@ def test_td_rfloordiv_invalid_scalar(self):
         # GH#18846
         td = Timedelta(hours=3, minutes=3)
 
-        dt64 = np.datetime64("2016-01-01", dtype="datetime64[us]")
+        dt64 = np.datetime64("2016-01-01", "us")
         with pytest.raises(TypeError):
             td.__rfloordiv__(dt64)
 

pandas/tests/scalar/timestamp/test_timestamp.py

@@ -575,15 +575,15 @@ def test_bounds_with_different_units(self):
 
         for date_string in out_of_bounds_dates:
             for unit in time_units:
-                dt64 = np.datetime64(date_string, dtype="M8[{unit}]".format(unit=unit))
+                dt64 = np.datetime64(date_string, unit)
                 with pytest.raises(ValueError):
                     Timestamp(dt64)
 
         in_bounds_dates = ("1677-09-23", "2262-04-11")
 
         for date_string in in_bounds_dates:
             for unit in time_units:
-                dt64 = np.datetime64(date_string, dtype="M8[{unit}]".format(unit=unit))
+                dt64 = np.datetime64(date_string, unit)
                 Timestamp(dt64)
 
     def test_min_valid(self):