style: Simplify code in tests

Author: ChrisChV

openedx/core/djangoapps/content_libraries/tests/test_containers.py

@@ -1074,11 +1074,12 @@ def test_container_draft_history_includes_descendant_components(self):
         history = self._get_container_draft_history(unit["id"])
         changed_at_list = [entry["changed_at"] for entry in history]
         # Both the container edit and the block edit should appear in the history.
-        assert block_edit_time.isoformat().replace("+00:00", "Z") in changed_at_list
-        assert container_edit_time.isoformat().replace("+00:00", "Z") in changed_at_list
+        block_edit_time_str = block_edit_time.isoformat().replace("+00:00", "Z")
+        container_edit_time_str = container_edit_time.isoformat().replace("+00:00", "Z")
+        assert block_edit_time_str in changed_at_list
+        assert container_edit_time_str in changed_at_list
         # History is sorted newest-first, so the block edit should come before the container edit.
-        assert changed_at_list.index(block_edit_time.isoformat().replace("+00:00", "Z")) < \
-               changed_at_list.index(container_edit_time.isoformat().replace("+00:00", "Z"))
+        assert changed_at_list.index(block_edit_time_str) < changed_at_list.index(container_edit_time_str)
 
     def test_container_draft_history_action_renamed(self):
         """