exports: Refactor event_time to export_time timestamp.

The time of the event was incorrectly being sent
as a datetime object.

zerver/lib/export.py

@@ -1709,7 +1709,7 @@ def get_realm_exports_serialized(user: UserProfile) -> List[Dict[str, Any]]:
     for export in all_exports:
         exports_dict[export.id] = dict(
             id=export.id,
-            event_time=export.event_time.ctime(),
+            export_time=export.event_time.timestamp(),
             acting_user_id=export.acting_user.id,
             extra_data=ujson.loads(export.extra_data)
         )

zerver/tests/test_events.py

@@ -2763,13 +2763,13 @@ class EventsRegisterTest(ZulipTestCase):
             ('type', equals('realm_export')),
             ('exports', check_list(check_dict_only([
                 ('id', check_int),
-                ('event_time', check_string),
+                ('export_time', check_float),
                 ('acting_user_id', check_int),
                 ('extra_data', check_dict_only([
                     ('export_path', check_string),
                     ('deleted_timestamp', equals(None))
                 ])),
-            ])))
+            ]))),
         ])
 
         do_change_is_admin(self.user_profile, True)