ci: pin peaceiris/actions-gh-pages action

Signed-off-by: Noam Gal <[email protected]>

Author: ATGardner

.github/workflows/docs.yaml

@@ -46,7 +46,7 @@ jobs:
           if-no-files-found: error
       - name: Publish to GH Pages (when on main)
         if: github.repository == 'argoproj/argo-workflows' && github.ref == 'refs/heads/main'
-        uses: peaceiris/actions-gh-pages@v3
+        uses: peaceiris/actions-gh-pages@373f7f263a76c20808c831209c920827a82a2847 # v3.9.3
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_branch: gh-pages