`build-arm64.yaml` reruns the 60-minute mainline kernel build on every push
to main. That's the right behavior when kernel fragments / init scripts /
build scripts change — it's pure burn when only workflows or docs do.
Add `paths-ignore` for `.gitea/workflows/**`, `.github/workflows/**`,
`docs/**`, top-level `*.md`, `CHANGELOG.md`, `README.md`, `.gitignore`.
Any change that affects what we build (kernel fragment, module list, init,
build/) still triggers a fresh run.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>