CI: mgmt-test-units always fails for upgrade from release 1.4 to 1.6

mgmt-test-units fails in the upgrade from release-1.4 to release-1.6 scenario.

sylvactl watch loops on:

failed to list source.toolkit.fluxcd.io/v1, Resource=ocirepositories: the server could not find the requested resource

Pipelines failed:

mgmt-test-units (#15948240772) · Jobs · Sylva-projects / sylva-core · GitLab

mgmt-test-units (#15925889903) · Jobs · Sylva-projects / sylva-core · GitLab

mgmt-test-units (#15919069160) · Jobs · Sylva-projects / sylva-core · GitLab

This happens because the management cluster is first deployed at release-1.4 and mgmt-test-units runs while the cluster is still at release-1.4, i.e., against Flux 2.5.1, which serves OCIRepository at v1beta2 only.

But mgmt-test-units uses the sylvactl bundled in the ci-job image, which watches OCIRepository at v1.