Enables back duplicate cancelling on push/schedule (#11471)

We disabled duplicate cancelling on push/schedule in #11397
but then it causes a lot of extra strain in case several commits
are merged in quick succession. The master merges are always
full builds and take a lot of time, but if we merge PRs
quickly, the subsequent merge cancels the previous ones.

This has the negative consequence that we might not know who
broke the master build, but this happens rarely enough to suffer
the pain at expense of much less strained queue in GitHub Actions.

.github/workflows/build-images-workflow-run.yml

@@ -71,7 +71,6 @@ jobs:
           cancelMode: duplicates
           sourceRunId: ${{ github.event.workflow_run.id }}
           notifyPRCancel: true
-          skipEventTypes: '["schedule", "push"]'
       - name: "Output BUILD_IMAGES"
         id: build-images
         run: |