Skip oci login if CI_REGISTRY variables are not set
On self-hosted GitLab the container registry could be disabled. In this case you see the the following error:
There are some problems with the CLI configuration:
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│ Error: Invalid oci_credentials block
│
│ The oci_credentials block at 3:20 has an invalid block label: invalid
│ reference: invalid registry "".
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I added a check for the CI_REGISTRY variables. If they are not set, the oci login will be skipped.