Fix flaky test

[sanchezl]

Fix the flakiness in TestResourceIndexedInformer.

[k8s-ci-robot]

Hi @sanchezl. Thanks for your PR.

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[caesarxuchao]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: caesarxuchao, sanchezl

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