Run tests on pipeline images on all arches

The pipeline image testing was only done on amd64.

These tests

• are already used for gating builder-rawhide/eln images to :production in the containers repo
• are going to be used for automatic merges of Renovate MRs

The lxml breakage on rawhide shows that some dependency issues will only show themselves on a single arch.

So increase test coverage across arches by running the unit and shellspec tests on all arches if:

• a pipeline was triggered via ONLY_IMAGE for a single image, as is the case for dependent pipelines
• dependencies are updated via the constraints.txt, as is the case for Renovate MRs

Part of kernel-ark#144 (closed)