Fixed branch names

Author: Andrews2024

.github/workflows/nightly-merge.yml

@@ -19,8 +19,8 @@ jobs:
     - name: Merge main into gh-pages 
       uses: robotology/gh-action-nightly-merge@v1.5.2
       with:
-        stable_branch: 'master'
-        development_branch: 'devel'
+        stable_branch: 'main'
+        development_branch: 'gh-pages'
         allow_ff: false
       env:
         GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}