[BP-1.12][FLINK-22577][tests] Harden KubernetesLeaderElectionAndRetrievalITCase

[tillrohrmann]

Backport of #15849 to release-1.12.

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[wangyang0918]

+1 for merging.

[tillrohrmann]

Thanks for the review @wangyang0918. The failing e2e test seems to be unrelated. Merging it now.

Merged via ed9965c