Allow PHPUnit build and Nightwatch jobs to retry once

Linking a related, and still open, issue that also discusses retrying known flakey tests. No decision is in this issue, and the issue predates GitLabCI.

I think this makes sense for now. It’s a small change, if it does not work it can be easily reverted.

In PHPUnit upstream, this is being proposed in #[Retry] attribute to support retrying flaky test #6182. That will allow working on a test class instead of the entire CI job, but surely will only happen in PHPUnit 12 or 13.