Merge branch 'group-milestones-breadcrumb' into 'master'

Fixes group milestones breadcrumb links

Closes #38781

See merge request gitlab-org/gitlab-ce!14689

app/views/groups/milestones/_header_title.html.haml

-- header_title group_title(@group, "Milestones", group_milestones_path(@group))
+- breadcrumb_title @milestone.title
+- add_to_breadcrumbs "Milestones", group_milestones_path(@group)

changelogs/unreleased/group-milestones-breadcrumb.yml

+---
+title: Fixed milestone breadcrumb links
+merge_request:
+author:
+type: fixed