Use retry option for GitLab CI jobs

GitLab has a retry option to retry CI jobs that have failed:

https://docs.gitlab.com/ee/ci/yaml/#retry

This would be useful to retry jobs that have failed due to e.g transient network outages installing prerequisites, or uploading artifacts, both of which happen often enough. It looks like the retry option can be configured to only retry certain job failures, so a build error would still result in an immediate failure.