chore: pr-linter/do-not-close never worked (#26762)

We have a label, `pr-linter/do-not-close` that has not been doing its job. See #26039.

It is because we are expecting a comma-separated-list, without spaces:

https://github.com/rix0rrr/close-stale-prs/blob/ffeb148adbaf7402e77bc4eafce8ed3d3c40f29c/src/index.ts#L22

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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

.github/workflows/close-stale-prs.yml

@@ -25,5 +25,5 @@ jobs:
           important-checks-regex: AutoBuildv2Project1C6BFA3F
           warn-message: This PR has been in the STATE state for 3 weeks, and looks abandoned. To keep this PR from being closed, please continue work on it. If not, it will automatically be closed in a week.
           close-message: This PR has been deemed to be abandoned, and will be automatically closed. Please create a new PR for these changes if you think this decision has been made in error.
-          skip-labels: contribution/core, pr-linter/do-not-close
+          skip-labels: contribution/core,pr-linter/do-not-close
           close-label: closed-for-staleness