CODEOWNERS: Add files which need Gitaly's approval

We've seen grown some inefficient access patterns in these files. In an
attempt to overcome more of these get added, make a few Gitaly people
--who are familiar with the Rails side of things-- code-owner of these
files so they will be asked for review when these files are touched.

Relates-to: https://gitlab.com/groups/gitlab-org/-/epics/5717

.gitlab/CODEOWNERS

@@ -334,3 +334,11 @@ Dangerfile @gl-quality/eng-prod
 
 [Application Security]
 /lib/gitlab/content_security_policy/ @gitlab-com/gl-security/appsec
+
+[Gitaly]
+lib/gitlab/git_access.rb @proglottis @toon @zj-gitlab
+lib/gitlab/git_access_*.rb @proglottis @toon @zj-gitlab
+ee/lib/ee/gitlab/git_access.rb @proglottis @toon @zj-gitlab
+ee/lib/ee/gitlab/git_access_*.rb @proglottis @toon @zj-gitlab
+ee/lib/ee/gitlab/checks/** @proglottis @toon @zj-gitlab
+lib/gitlab/checks/** @proglottis @toon @zj-gitlab