UPSTREAM: 1873: evictions: fix assumePod silently dropping success metric on informer race

[ingvagabund]

When KubeVirt sets EvictionInProgressAnnotationKey before returning TooManyRequests, the informer's UpdateFunc can call addPod (evictionAssumed=false) before evictPod's assumePod call arrives. assumePod found the entry already present and returned early, leaving evictionAssumed=false. DeleteFunc then skipped the "success" metric.

Fix: if the existing entry has evictionAssumed=false (added by addPod), upgrade it in place without double-counting the pod in the counters.

Adds TestEvictionInBackgroundMetrics_InformerRace to reproduce the race deterministically.

Pulling kubernetes-sigs#1873.

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[openshift-ci]

@ingvagabund: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/security	3f3be90	link	false	/test security

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[tiraboschi]

/lgtm

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ingvagabund, tiraboschi

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[tiraboschi]

/cherry-pick main

[openshift-cherrypick-robot]

@tiraboschi: new pull request created: #789

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/cherry-pick main

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