charm-update-libs fails on repositories with issues disabled

[pedro-avalos]

There are some repositories for which issues are tracked outside of GitHub (e.g., private repositories). These issues could still benefit from the charm-update-libs.yml workflow, but fail to run it because the workflow exits when it cannot find issues.

I can think of a couple solutions:

1. Add option to disable issues step for these repositories, and expect these repositories to rely on PR library check
2. If gh issue list --limit 1 command yields the '<owner>/<repo>' repository has disabled issues, then create a warning and skip the step