[CI] Add a retry to unit test jobs

What does this MR do?

[CI] Add a retry to unit test jobs

Specifies 1 retry if a unit test job fails.

This is intended as a temporary workaround while we address:

• #764 (closed)
• #883 (closed)

We end up getting lots of issues created by issue-bot due to these tests failing, and they almost always pass on a retry.

Test plan

See this job, which failed and was automatically retried.

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Required

• Merge Request Title and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• When ready for review, MR is labeled "~workflow::ready for review" per the Distribution MR workflow

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for omnibus-gitlab opened
• Validate potential values for new configuration settings. Formats such as integer 10, duration 10s, URI scheme://user:passwd@host:port may require quotation or other special handling when rendered in a template and written to a configuration file.

Related issues

* https://gitlab.com/gitlab-org/cloud-native/gitlab-operator/-/issues/764
* https://gitlab.com/gitlab-org/cloud-native/gitlab-operator/-/issues/883