Make referee external-plugin acknowledge skip-review on pull requests in the same way as for lgtm/approved PRs

[dhiller]

We need to make referee stop pull requests that are marked with skip-review label in the same way as we do for lgtm/approved, otherwise it will retest forever.

See original conversation for context:

Hi @dhiller i am not sure it is good to have skip-review on kubevirtci bumps, as it can mask real new problems by retest

You're right, we probably need to update the referee bot to also account for PRs with label skip-review and hold them in the same way.

Originally posted by @dhiller in kubevirt/kubevirt#16294 (comment)

[dhiller]

FYI @dollierp @Whitedyl

[dhiller]

This needs a more thorough investigation, I did a quick check and it seems from looking at the code this shouldn't happen.

/triage needs-information