BUG: Adds missing raises for numpy.timedelta64[M/Y] in pandas.Timedelta

pandas/_libs/tslibs/timedeltas.pyx

@@ -1739,8 +1739,10 @@ class Timedelta(_Timedelta):
                 + int(kwargs.get("milliseconds", 0) * 1_000_000)
                 + seconds
             )
-
-        if unit in {"Y", "y", "M"}:
+        if unit in {"Y", "y", "M"} or (isinstance(value, np.timedelta64) and
+                                       get_datetime64_unit(value) in {
+                                        NPY_DATETIMEUNIT.NPY_FR_Y,
+                                        NPY_DATETIMEUNIT.NPY_FR_M}):
             raise ValueError(
                 "Units 'M', 'Y', and 'y' are no longer supported, as they do not "
                 "represent unambiguous timedelta values durations."

pandas/tests/libs/test_lib.py

@@ -58,7 +58,7 @@ def test_fast_multiget_timedelta_resos(self):
         tm.assert_numpy_array_equal(result, expected)
 
         # case that can't be cast to td64ns
-        td = Timedelta(np.timedelta64(400, "Y"))
+        td = Timedelta(np.timedelta64(146000, "D"))
         assert hash(td) == hash(td.as_unit("ms"))
         assert hash(td) == hash(td.as_unit("us"))
         mapping1 = {td: 1}

pandas/tests/scalar/timedelta/test_constructors.py

@@ -289,7 +289,6 @@ def test_overflow_on_construction():
 @pytest.mark.parametrize(
     "val, unit",
     [
-        (3508, "M"),
         (15251, "W"),  # 1
         (106752, "D"),  # change from previous:
         (2562048, "h"),  # 0 hours
@@ -333,7 +332,6 @@ def test_construction_out_of_bounds_td64ns(val, unit):
 @pytest.mark.parametrize(
     "val, unit",
     [
-        (3508 * 10**9, "M"),
         (15251 * 10**9, "W"),
         (106752 * 10**9, "D"),
         (2562048 * 10**9, "h"),