add extra test case in the test_constructor_str_infer_reso (#52199)

add extra test case

Author: natmokval

pandas/tests/scalar/timestamp/test_constructors.py

@@ -58,6 +58,12 @@ def test_constructor_str_infer_reso(self):
         ts = Timestamp("2016 June 3 15:25:01.345")
         assert ts.unit == "ms"
 
+        ts = Timestamp("300-01-01")
+        assert ts.unit == "s"
+
+        ts = Timestamp("300 June 1:30:01.300")
+        assert ts.unit == "ms"
+
     def test_constructor_from_iso8601_str_with_offset_reso(self):
         # GH#49737
         ts = Timestamp("2016-01-01 04:05:06-01:00")