Add stale package relation cleanup to offboarding

Otherwise the page tends to get cluttered up with inactive users.

.gitlab/issue_templates/Offboarding.md

@@ -40,6 +40,7 @@ This template should be used for offboarding Arch Linux team members.
 - [ ] Remove member from [arch-tu](https://lists.archlinux.org/mailman3/lists/arch-tu.lists.archlinux.org/members/member/) and/or [arch-dev](https://lists.archlinux.org/mailman3/lists/arch-dev.lists.archlinux.org/members/member/) mailing lists.
 - [ ] Ask the user to leave `#archlinux-tu` and/or `#archlinux-dev` on Libera Chat and forget the password(s).
 - [ ] Create an issue in [archlinux-keyring](https://gitlab.archlinux.org/archlinux/archlinux-keyring) using the [*"Remove Packager Key"*](https://gitlab.archlinux.org/archlinux/archlinux-keyring/-/issues/new?issuable_template=Remove%20Packager%20Key) template.
+- [ ] Remove [stale package relations](https://archlinux.org/packages/stale_relations/) for the now inactive user.
 
 ## DevOps offboarding checklist