Make tests pass some more years (#3045)

Without this patch, tests fail after 2024-11-25.

Background:
As part of my work on reproducible builds for openSUSE, I check that
software still gives identical build results in the future.
The usual offset is +16 years, because that is how long I expect some
software will be used in some places.
This showed up failing tests in our python-PyGithub package build.
See https://reproducible-builds.org/ for why this matters.

---------

Co-authored-by: Enrico Minack <github@enrico.minack.dev>

Author: Bernhard M. Wiedemann

tests/Authentication.py

@@ -176,16 +176,15 @@ def testAppInstallationAuthAuthentication(self):
         installation_auth = github.Auth.AppInstallationAuth(self.app_auth, 29782936)
         g = github.Github(auth=installation_auth)
 
-        # test token expiry
         # token expires 2024-11-25 01:00:02
         token = installation_auth.token
-        self.assertFalse(installation_auth._is_expired)
         self.assertEqual(
             installation_auth._AppInstallationAuth__installation_authorization.expires_at,
             datetime(2024, 11, 25, 1, 0, 2, tzinfo=timezone.utc),
         )
 
-        # forward the clock so token expires
+        # test token expiry
+        # control the current time used by _is_expired
         with mock.patch("github.Auth.datetime") as dt:
             # just before expiry
             dt.now = mock.Mock(return_value=datetime(2024, 11, 25, 0, 59, 3, tzinfo=timezone.utc))
@@ -204,9 +203,9 @@ def testAppInstallationAuthAuthentication(self):
                 datetime(2025, 11, 25, 1, 0, 2, tzinfo=timezone.utc),
             )
 
-        # use the token
-        self.assertEqual(g.get_user("ammarmallik").name, "Ammar Akbar")
-        self.assertEqual(g.get_repo("PyGithub/PyGithub").full_name, "PyGithub/PyGithub")
+            # use the token
+            self.assertEqual(g.get_user("ammarmallik").name, "Ammar Akbar")
+            self.assertEqual(g.get_repo("PyGithub/PyGithub").full_name, "PyGithub/PyGithub")
 
     def testAppInstallationAuthAuthenticationRequesterArgs(self):
         installation_auth = github.Auth.AppInstallationAuth(self.app_auth, 29782936)