Bump dieghernan/cff-validator from 3 to 4

Bumps [dieghernan/cff-validator](https://github.com/dieghernan/cff-validator) from 3 to 4.
- [Release notes](https://github.com/dieghernan/cff-validator/releases)
- [Changelog](https://github.com/dieghernan/cff-validator/blob/main/CHANGELOG.md)
- [Commits](dieghernan/cff-validator@v3...v4)

---
updated-dependencies:
- dependency-name: dieghernan/cff-validator
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

.github/workflows/linux.yml

@@ -46,7 +46,7 @@ jobs:
 
     - name: Validate CITATION.cff
       if: matrix.build_type == 'full' && github.event_name == 'schedule' && matrix.compiler == 'gcc'
-      uses: dieghernan/cff-validator@v3
+      uses: dieghernan/cff-validator@v4
       with:
         install-r: true
         citation-path: sumo/CITATION.cff