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Makes tidy check commit messages since the latest merge, failing if one of them contains the string "WIP".
I have written a test for my changes, although it is a bit hacky.
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<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix#14388.
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- [x] These changes do not require tests because this would require playing with a new/existing git repo
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Source-Repo: https://github.com/servo/servo
Source-Revision: da15790e41b9404845bec9ae4dcdc127d23fa8ca
e2a2969d6e