build(deps): bump theupdateframework/tuf-on-ci in the actions group

Bumps the actions group with 1 update: [theupdateframework/tuf-on-ci](https://github.com/theupdateframework/tuf-on-ci).


Updates `theupdateframework/tuf-on-ci` from 0.14.0 to 0.15.1
- [Release notes](https://github.com/theupdateframework/tuf-on-ci/releases)
- [Changelog](https://github.com/theupdateframework/tuf-on-ci/blob/main/docs/CHANGELOG.md)
- [Commits](theupdateframework/tuf-on-ci@fce107e...fffb59f)

---
updated-dependencies:
- dependency-name: theupdateframework/tuf-on-ci
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: actions
...

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

.github/workflows/reusable-prober.yml

@@ -123,7 +123,7 @@ jobs:
         run: cp "${{ inputs.tuf_root_path }}" ./root.json
 
       - name: Verify TUF repository state
-        uses: theupdateframework/tuf-on-ci/actions/test-repository@fce107eeb8b1887239ca3a694dc250fcabf49c7f # v0.14.0
+        uses: theupdateframework/tuf-on-ci/actions/test-repository@fffb59fa10497d72f0e3df531b88b3c5adf868fe # v0.15.1
         with:
           metadata_url: ${{ inputs.tuf_repo }}
           valid_days: 2
@@ -133,7 +133,7 @@ jobs:
 
       - name: Verify preprod TUF repository state (and the upgrade from prod)
         if: ${{ inputs.enable_staging == false }}
-        uses: theupdateframework/tuf-on-ci/actions/test-repository@fce107eeb8b1887239ca3a694dc250fcabf49c7f # v0.14.0
+        uses: theupdateframework/tuf-on-ci/actions/test-repository@fffb59fa10497d72f0e3df531b88b3c5adf868fe # v0.15.1
         with:
           metadata_url: ${{ inputs.tuf_preprod_repo }}
           update_base_url:  ${{ inputs.tuf_repo }}