fix(ci): skip Docker Hub login on pull_request events

Dependabot PRs cannot access repository secrets, causing the login step
to fail with 'Username and password required'. Since the build-push step
already skips push on PRs, the login is also unnecessary for PRs.

Author: paoloronco

.github/workflows/docker-publish.yml

@@ -36,6 +36,7 @@ jobs:
             type=raw,value=latest,enable={{is_default_branch}}
 
       - name: Login to Docker Hub
+        if: github.event_name != 'pull_request'
         uses: docker/login-action@v3
         with:
           username: ${{ secrets.DOCKERHUB_USERNAME }}
@@ -54,4 +55,3 @@ jobs:
             NODE_ENV=production
           cache-from: type=registry,ref=paueron/lynx:buildcache
           cache-to: type=inline
-