Fixed pkgdown GHA

Author: VisruthSK

.github/workflows/pkgdown.yaml

@@ -69,4 +69,4 @@ jobs:
           git config --global user.email "${{ github.actor }}@users.noreply.github.com"
           git add docs
           git commit -m "Build and deploy pkgdown site [ci skip]" || exit 0
-          git push origin HEAD:${{ github.ref_name }}
+          git push origin HEAD:master