ci: build docker image on pull request without pushing

Author: RaniAgus

.github/workflows/publish-docker-image.yml

@@ -11,6 +11,9 @@ on:
     tags:
       - v*
 
+  # Run tests for any PRs.
+  pull_request:
+
 env:
   IMAGE_NAME: cspec-alpine
 
@@ -33,10 +36,12 @@ jobs:
         run: docker build . --file Dockerfile --tag $IMAGE_NAME --label "runnumber=${GITHUB_RUN_ID}"
 
       - name: Log in to registry
+        if: github.event_name == 'push'
         # This is where you will update the PAT to GITHUB_TOKEN
         run: echo "${{ secrets.GITHUB_TOKEN }}" | docker login ghcr.io -u ${{ github.actor }} --password-stdin
 
       - name: Push image
+        if: github.event_name == 'push'
         run: |
           IMAGE_ID=ghcr.io/${{ github.repository_owner }}/$IMAGE_NAME