There's something goofy going on. When configuring a job to reference a Git repository, and choosing an associated SSH+Key credential for access, we're seeing the following after choosing the right credential. However, ignoring this red error in the UI, saving the job configuration, and using those configured credentials works fine. More strangeness described after the error below:

Failed to connect to repository : Command "git ls-remote -h git@gitlab.our.org:r701-cookbooks/r701-redhat-subs.git HEAD" returned status code 128:
stdout:
stderr: Permission denied, please try again.
Permission denied, please try again.
Received disconnect from xx.xx.10.102: 2: Too many authentication failures for git
fatal: The remote end hung up unexpectedly

This is of course gives users the idea that their credentials are wrong or broken, so they then go off wasting time on something that isn't a problem.

The other strangeness, is that if we see this error (before saving), and try to "re-toggle" our right credentials by selecting "-- none --", the UI resets the selection to the credentials we'd previously set.

That is:

1. Brand new job
2. Chose "Git"
3. Type repo as git@gitlab.our.org:whatever/our-repo.git
4. Change '-- none --' credential to 'jblaine Gitlab SSH key'
5. Red error shown above shows. If we saved right now, the 'jblaine Gitlab SSH key' credentials chosen would in fact work fine to do the clone during the job build.
6. Change 'jblaine Gitlab SSH key' credential selection to '-- none --'
7. It immediately gets set back to 'jblaine Gitlab SSH key'
8. Change 'jblaine Gitlab SSH key' credential selection to '-- none --'. It STAYS this time.
9. Change '-- none --' credential to 'jblaine Gitlab SSH key'
10. Get the red error above...
11. Give up and click Save.
12. Build job. It works fine.