Don't have Wingetbot retry Validation-Completed when blocking label is present

[Trenly]

Description of the new feature/enhancement

When the Needs-Attention, Changes-Requested, Blocking-Issue, or Needs-Author-Feedback label is present on a PR, the policy service will not approve the PR even if the pipeline has completed successfully.

There is logic in Wingetbot to re-add the Validation-Completed label to ensure that any PRs which can be approved don't get into a stuck state due to a webhook outage or an API rate limit. However, as seen in #141254 it will attempt to re-add the label even when there are conditions which would prevent the Policy Service from being able to approve. This eats up API requests to remove and re-add the label, and can be confusing to users who don't understand why the label is being constantly re-applied.

Therefore, if any of the blocking labels are present on the PR, wingetbot should not remove and re-add the Validation-Completed label

Proposed technical implementation details (optional)

No response