Conditional `required` checks (#4544)
Workaround for skipped but `required` github checks. The idea is to trigger the workflow but filter out unaffected jobs or steps. See [ci_cd 998](https://github.com/paritytech/ci_cd/issues/988) for details In `.github/workflows/check-changed-files.yml` there is a reusable workflow thad does all the checks and publishes results as outputs. Example usage: ``` jobs: changes: permissions: pull-requests: read uses: ./.github/workflows/check-changed-files.yml some-job: needs: changes if: ${{ needs.changes.outputs.rust }} ....... ```