Enable mmap_stats GME probe

What does this MR do and why?

We added a new probe (mmap_stats) to GME
Context: #385442 (closed)

To enable it, we need to:

• bump GME version (I am pointing to this commit)
• add a new probe to the list

How to set up and validate locally

1. Checkout this branch 385442-enable-mmap-stats-probe-gme
2. Go to GME dir in GDK, in my case: cd /Users/al/dev/gitlab-development-kit/gitlab-metrics-exporter
3. Checkout the target GME commit: git checkout 65bbfa0b62518691961de096e4a27d7c76307b7c
4. Build the GME binary: make
5. Make sure https://gitlab.com/gitlab-org/gitlab/-/blob/master/config/initializers/7_prometheus_metrics.rb#L29 returns true or hack it to return true (by default, my GDK is configured the way it returns false)
6. (Re-)Start GDK: GITLAB_GOLANG_METRICS_SERVER=1 gdk restart. Make sure GITLAB_GOLANG_METRICS_SERVER ENV var is set.
7. Visit http://localhost:8083/metrics
8. Make sure two new gauges are present:

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #385442 (closed)