Gracefully exit from escalation workers on failure

What does this MR do?

Related issue: #337259 (closed)

IncidentManagement::PendingEscalations::AlertCheckWorker and IncidentManagement::PendingEscalations::AlertCreateWorker both raise errors when the input object ids don't correspond an existing record. In that scenario, we wouldn't expect those records to ever exist, so we should just return from the worker silently. Otherwise, the job will be continually retried, even though we never expect it to be successful.

Does this MR meet the acceptance criteria?

Conformity

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Security

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