Bumps mailroom to 0.9.1
Mailroom is already set to this version in 12.3, we should update the charts so it matches https://gitlab.com/gitlab-org/gitlab/blob/12-3-stable-ee/Gemfile#L414
Mailroom is already set to this version in 12.3, we should update the charts so it matches https://gitlab.com/gitlab-org/gitlab/blob/12-3-stable-ee/Gemfile#L414