fix: add missing quotes in plugin-config

Author: Nylle

.github/workflows/publish-to-maven-central.yml

@@ -29,7 +29,7 @@ jobs:
       - name: Generate settings.xml
         uses: whelk-io/maven-settings-xml-action@v22
         with:
-          servers: '[{ "id": "central", "username": ${{ secrets.NEXUS_USERNAME }}, "password": ${{ secrets.NEXUS_PASSWORD }} }]'
+          servers: '[{ "id": "central", "username": "${{ secrets.NEXUS_USERNAME }}", "password": "${{ secrets.NEXUS_PASSWORD }}" }]'
 
       - name: Release Maven package
         uses: WasiqB/maven-publish-action@v1