Merge branch 'docs/release-notes' of https://github.com/opf/openproject…

… into docs/release-notes

docs/release-notes/13-4-0/README.md

@@ -39,7 +39,7 @@ With this integration, you can manage GitLab's units of work (merge requests and
 
 Before upgrading, please do the following:
 
-1. Remove traces of the GitLab integration in your **Gemfile.lock** and **Gemfile.modules**. See [btey/openproject-gitlab-integration#configuration](https://github.com/btey/openproject-gitlab-integration?tab=readme-ov-file#configuration)
+1. Remove traces of the GitLab integration in your **Gemfile.lock** and **Gemfile.modules**. See [btey/openproject-gitlab-integration#configuration](https://github.com/btey/openproject-gitlab-integration?tab=readme-ov-file#configuration) Failure to do so may result in a `Bundler::GemfileError` matching the following error message: _Your Gemfile lists the gem openproject-gitlab_integration (>= 0) more than once._
 2. Remove the module code traces of the GitLab integration by running this command: `rm -rf /path/to/openproject/modules/gitlab_integration` 
 
 </div>