gh-37950: CI: Handle the "p: CI Fix" label
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As decided by vote in https://groups.google.com/g/sage-
devel/c/OKwwUGyKveo/m/vpyCXYBqAAAJ (2024-03).
The only change here is to change the search from open PRs with "p:
blocker / 1" labels to those with "p: CI Fix" labels.
No attempt is made to take any status labels into account. All open PRs
with the "p: CI Fix" label are processed.
### :memo: Checklist
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- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
- [x] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation and checked the documentation
preview.
### :hourglass: Dependencies
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<!-- - #12345: short description why this is a dependency -->
<!-- - #34567: ... -->
URL: https://github.com/sagemath/sage/pull/37950
Reported by: Matthias Köppe
Reviewer(s): Frédéric Chapoton
