(mgmt|wkld)-image-ref-report breaks in CI

In CI jobs (mgmt|wkld)-image-ref-report break with this error:

Traceback (most recent call last):
  File "/builds/sylva-projects/sylva-core/./tools/get_image_refs.py", line 664, in <module>
    main()
  File "/builds/sylva-projects/sylva-core/./tools/get_image_refs.py", line 617, in main
    matched_units = match_unit_from_rules(image, unit_mapping_rules)
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/builds/sylva-projects/sylva-core/./tools/get_image_refs.py", line 516, in match_unit_from_rules
    for rule in rules:
                ^^^^^
TypeError: 'NoneType' object is not iterable

(e.g. https://gitlab.com/sylva-projects/sylva-core/-/jobs/10462131126)

This seems to be due to the merge of !4638 (merged)