Dependency(deps): Bump whelk-io/maven-settings-xml-action from 20 to 21

Bumps [whelk-io/maven-settings-xml-action](https://github.com/whelk-io/maven-settings-xml-action) from 20 to 21.
- [Release notes](https://github.com/whelk-io/maven-settings-xml-action/releases)
- [Commits](https://github.com/whelk-io/maven-settings-xml-action/compare/v20...v21)

---
updated-dependencies:
- dependency-name: whelk-io/maven-settings-xml-action
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/publish.yml

@@ -14,7 +14,7 @@ jobs:
           java-version: '17'
           distribution: 'temurin'
       - name: Set maven settings.xml
-        uses: whelk-io/maven-settings-xml-action@v20
+        uses: whelk-io/maven-settings-xml-action@v21
         with:
           servers: '[{ "id": "ossrh", "username": "jplag", "password": "${{ secrets.OSSRH_TOKEN }}" }]'
       - name: Import GPG key