There's a closed pull request on the void-packages repository

.github/workflows/cycles.yaml: run on PRs, don't run on forks
https://github.com/void-linux/void-packages/pull/45933

Description:
- running on forks is kinda useless and just gives people useless error messages if they sync their master branch at the wrong time
- run cycle check on PRs to catch cycles before they happen. this makes the cron cycle check more of a backup/just-in-case for things that slip past the CI

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#### Testing the changes
- I tested the changes in this PR: **YES**|**briefly**|**NO**