Add GithubObject.last_modified_datetime to have last_modified as …

…a `datetime` (#2772)

github/GithubObject.py

@@ -312,6 +312,13 @@ def last_modified(self) -> Optional[str]:
         """
         return self._headers.get(Consts.RES_LAST_MODIFIED)  # type: ignore
 
+    @property
+    def last_modified_datetime(self) -> Optional[datetime]:
+        """
+        :type: datetime
+        """
+        return self._makeDatetimeAttribute(self.last_modified).value  # type: ignore
+
     def get__repr__(self, params: Dict[str, Any]) -> str:
         """
         Converts the object to a nicely printable string.

tests/GithubObject.py

@@ -23,7 +23,7 @@
 import unittest
 from datetime import datetime, timedelta, timezone
 
-from dateutil.tz.tz import tzoffset
+from dateutil.tz.tz import tzoffset, tzutc
 
 from . import Framework
 
@@ -78,6 +78,10 @@ def testMakeDatetimeAttribute(self):
                 "2021-01-23T12:34:56.000-06:00",
                 datetime(2021, 1, 23, 12, 34, 56, tzinfo=tzoffset(None, -21600)),
             ),
+            (
+                "Mon, 11 Sep 2023 14:07:29 GMT",
+                datetime(2023, 9, 11, 14, 7, 29, tzinfo=tzutc()),
+            ),
         ]:
             actual = gho.GithubObject._makeDatetimeAttribute(value)
             self.assertEqual(gho._ValuedAttribute, type(actual), value)