bug in get_image_refs.py

https://gitlab.com/sylva-projects/sylva-core/-/jobs/14592049116#L179

$ python3 ./tools/get_image_refs.py --kubeconfig management-cluster-kubeconfig --output ${CI_PROJECT_DIR}/image_refs_${CLUSTER}_${CI_PIPELINE_ID}.json --unit-mapping-config ./tools/unit_mapping_rules.yml
Started...
Traceback (most recent call last):
  File "/builds/sylva-projects/sylva-core/./tools/get_image_refs.py", line 101, in __init__
    self.set_registry_mirrors_mapping()         # sets the mapping based on the contents of the sylva-units-values
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/builds/sylva-projects/sylva-core/./tools/get_image_refs.py", line 647, in set_registry_mirrors_mapping
    if mirrors and mirrors['hosts_config']:
                   ~~~~~~~^^^^^^^^^^^^^^^^
KeyError: 'hosts_config'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "/builds/sylva-projects/sylva-core/./tools/get_image_refs.py", line 1205, in <module>
    main()
  File "/builds/sylva-projects/sylva-core/./tools/get_image_refs.py", line 1034, in main
    k8s_parser = K8sParser(kubeconfig=args.kubeconfig, workload_kubeconfig=args.workload_kubeconfig, workload_name=args.workload_name)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/builds/sylva-projects/sylva-core/./tools/get_image_refs.py", line 106, in __init__
    raise Exception(f"Error: {e}")
Exception: Error: 'hosts_config'