Update prometheus/client_golang to 1.12.1

Jacob Vosmaerrequested to merge
jv-update-prometheus into master

The previous version was 1.11.0.

This upgrade gives us a fix for CVE-2022-21698. We already have a defence in place for this issue at the application level but this solves the problem in Prometheus itself.

See also https://gitlab.com/gitlab-org/labkit/-/issues/29#note_857804311

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