[github-actions] Cert_5_3_05_RoutingLinkQuality.py fails intermittently

[jwhui]

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FAIL: test (__main__.Cert_5_3_5_RoutingLinkQuality)
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Traceback (most recent call last):
  File "/home/runner/work/openthread/openthread/examples/../tests/scripts/thread-cert/Cert_5_3_05_RoutingLinkQuality.py", line 104, in test
    self.assertTrue(self.nodes[ROUTER3].ping(leader_rloc))
AssertionError: False is not true

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https://github.com/openthread/openthread/actions/runs/3061813605/jobs/4942052869

[abtink]

+1 I have also noticed this test failing (similar error) more frequently lately.

[jwhui]

https://github.com/openthread/openthread/actions/runs/3228459474/jobs/5284585551

[jwhui]

https://github.com/openthread/openthread/actions/runs/3277136161/jobs/5394028879