Update Publish to GitHub Pages step (#95)

Use the new grails/github-pages-deploy-action which allow updating root index.html page

Author: puneetbehl

.github/workflows/gradle.yml

@@ -62,7 +62,7 @@ jobs:
           arguments: docs:docs
       - name: Publish to Github Pages
         if: steps.docs.outcome == 'success' && github.event_name == 'push'
-        uses: micronaut-projects/github-pages-deploy-action@master
+        uses: grails/github-pages-deploy-action@v2
         env:
           TARGET_REPOSITORY: ${{ github.repository }}
           GH_TOKEN: ${{ secrets.GH_TOKEN }}