Merge branch 'marcia-docs-fix-mark-as-viewed-gl-version' into 'master'

Update GL version for "mark file as viewed"

See merge request gitlab-org/gitlab!52898

doc/user/project/merge_requests/reviewing_and_managing_merge_requests.md

@@ -145,7 +145,7 @@ whitespace changes.
 
 ## Mark files as viewed
 
-> - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/51513) in GitLab 13.8.
+> - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/51513) in GitLab 13.9.
 > - It's deployed behind a feature flag, enabled by default.
 > - It's enabled on GitLab.com.
 > - It's recommended for production use.