[ci skip] Fix wrong secret

Author: DRSchlaubi

.github/workflows/ci.yml

@@ -26,7 +26,7 @@ jobs:
       - name: Publish Plugin
         if: github.ref == 'refs/heads/main'
         env:
-          MAVEN_USERNAME: ${{ vars.MAVEN_USERNAME }}
+          MAVEN_USERNAME: ${{ secrets.MAVEN_USERNAME }}
           MAVEN_PASSWORD: ${{ secrets.MAVEN_PASSWORD }}
           # TODO: add publishPlugins task
         run: ./gradlew publish