force image promotion with empty PR

[mvinkler]

Force image promotion to CI which should fix periodic-image-mirroring-knative job:

 Running: oc image mirror --dry-run=false --keep-manifest-list -f=/etc/imagemirror/mapping_knative_knative-v1.14_backstage-plugins_quay --skip-multiple-scopes
error: unable to retrieve source image registry.ci.openshift.org/openshift/knative-backstage-plugins-eventmesh by tag knative-v1.14: manifest unknown: manifest unknown
error: unable to retrieve source image registry.ci.openshift.org/openshift/knative-backstage-plugins-migrate by tag knative-v1.14: manifest unknown: manifest unknown
error: unable to retrieve source image registry.ci.openshift.org/openshift/knative-backstage-plugins-source-image by tag knative-v1.14: manifest unknown: manifest unknown
error: unable to retrieve source image registry.ci.openshift.org/openshift/knative-backstage-plugins-test-eventshub by tag knative-v1.14: manifest unknown: manifest unknown
error: an error occurred during planning
ERROR: Failed to mirror images from /etc/imagemirror/mapping_knative_knative-v1.14_backstage-plugins_quay 

[mgencur]

/lgtm

[openshift-ci]

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