regression in get-openstack-images / oci-tools / python oras

Yesterday we merged !4157 (merged) to incorporate in particular fixes to the Python oras library to solve #2256 (closed).

Unfortunately we observed a regression, with get-openstack-images failing with the following error when oci_registry_insecure: true is used.

2025-03-27 16:44:40,101 INFO oras.logger text_handler:
 Retrying in 3 seconds - error:
 HTTPSConnectionPool(host='172.20.136.39', port=443):
 Max retries exceeded with url:
 /service/token?service=harbor-registry&scope=repository%3Asylva.stable.diod%2Fotc-caas-images%2Fsle-15-6-hardened-rke2-1-30-9%3Apull
 (Caused by SSLError(SSLCertVerificationError(1, '[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate (_ssl.c:1006)')))

It seems like oci_registry_insecure: true isn't honored anymore with the newer python oras library, and the connection is attempted with a TLS check.

/cc @jonathang @mihai.zaharia @rletrocquer