Merge branch 'mr-sidebar-scroll' into 'master'

Let merge request sidebar scroll

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/149940



Merged-by: Phil Hughes <me@iamphill.com>
Approved-by: Chad Lavimoniere <clavimoniere@gitlab.com>
Approved-by: Sascha Eggenberger <seggenberger@gitlab.com>
Approved-by: Phil Hughes <me@iamphill.com>
Co-authored-by: Annabel Dunstone Gray <annabel.dunstone@gmail.com>