Backport PR #8165: use >= instead of > when comparing dates

fast test runners can result in equal values.

IPython/html/services/contents/tests/test_manager.py

@@ -271,7 +271,7 b' class TestContentsManager(TestCase):'
 
         # Reload notebook and verify that last_modified incremented.
         saved = cm.get(path)
-        self.assertGreater(saved['last_modified'], model['last_modified'])
+        self.assertGreaterEqual(saved['last_modified'], model['last_modified'])
 
         # Move the notebook and verify that last_modified stayed the same.
         # (The frontend fires a warning if last_modified increases on the