#49552: ci: rework reapply patches
Description of Change
#49516 didn't survive first contact, due to some flawed assumptions. gh run rerun will fail if the job/workflow is already running, and you can't cancel an individual job, only a full workflow. That means the previous approach of having apply-patches as a job inside the build.yml workflow isn't workable because there's no way to cancel and re-run just that job without canceling the whole workflow, and we want to avoid re-running the full build.
This PR reworks the approach to put apply-patches in a new workflow that runs against PRs that touch patches or DEPS, and updates rerun-apply-patches.yml to cancel the workflow if it's in-progress, wait for it to finish canceling, and then rerun the whole workflow.
Checklist
- PR description included
Release Notes
Notes: none
Backports
Semver Impact
Semantic Versioning helps users understand the impact of updates:
- Major (X.y.z): Breaking changes that may require code modifications
- Minor (x.Y.z): New features that maintain backward compatibility
- Patch (x.y.Z): Bug fixes that don't change the API
- None: Changes that don't affect using facing parts of Electron