workflow: don't push Docker container on PR

[blocktrron]

The docker container on PR action is broken in case the PR is not opened within the Gluon project.

Remove the build on PR so the pipeline does not fail for third party PRs.

[neocturne]

Hmm, optimally, we'd build the container (so the build is checked for PRs), but don't attempt to push it. Not sure if there is any simple way to achieve that.

[herbetom]

Something like the following? (sorry, github doesn't allow to do this as a suggestion)

      - name: Build Docker image
        if: github.event_name == 'pull_request'
        uses: docker/build-push-action@f2a1d5e99d037542a71f64918e516c093c6f3fc4
        with:
          context: ./contrib/docker
          push: false
          tags: ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}
      - name: Build and push Docker image
        if: github.event_name != 'pull_request'
        uses: docker/build-push-action@f2a1d5e99d037542a71f64918e516c093c6f3fc4
        with:
          context: ./contrib/docker
          push: true
          tags: ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}

Hoewer, this is only one potential half of what's required. In a fork the action would still fail because the destination of the push is still hardcoded.

[neocturne]

Something like the following? (sorry, github doesn't allow to do this as a suggestion)

      - name: Build Docker image
        if: github.event_name == 'pull_request'
        uses: docker/build-push-action@f2a1d5e99d037542a71f64918e516c093c6f3fc4
        with:
          context: ./contrib/docker
          push: false
          tags: ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}
      - name: Build and push Docker image
        if: github.event_name != 'pull_request'
        uses: docker/build-push-action@f2a1d5e99d037542a71f64918e516c093c6f3fc4
        with:
          context: ./contrib/docker
          push: true
          tags: ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}

Hoewer, this is only one potential half of what's required. In a fork the action would still fail because the destination of the push is still hardcoded.

Hmm, maybe it would even be possible to set the value of push depending on the condition, rather than duplicating the whole section?

[blocktrron]

I'd remove it for now so the CI won't complain. Can someone create a PR with the suggested changes so we can verify they work as expected?