devel/rubygem-prometheus-client-mmap: update to 0.19.1

Required for gitlab-ce 15.10.

Changelog:
https://gitlab.com/gitlab-org/ruby/gems/prometheus-client-mmap/-/blob/master/CHANGELOG.md
(cherry picked from commit 5180b66cb9af8898e460fa3e89b47eed92104ab4)