Update our omnibus gem to a version with more debug information

What does this MR do?

Updates our omnibus fork to the latest patch of ours, that includes some additional debug info when checksums fail: omnibus!16 (merged)

Example build with the additional output: https://dev.gitlab.org/gitlab/omnibus-gitlab/-/jobs/8982932#L5940

Related issues

Relates to gitlab-org/distribution/team-tasks#351 (closed)

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
• Pipeline is green on dev.gitlab.org if the change is touching anything besides documentation or internal cookbooks
• trigger-package has a green pipeline running against latest commit

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 the GitLab Chart opened