Update milestone issue list limit documentation

doc/administration/instance_limits.md

@@ -147,11 +147,11 @@ limited to 1KiB, and descriptions (the rest of the message) will be limited to
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/39453) in GitLab 12.10.
 
-The maximum number of issues loaded on the milestone overview page is 3000.
+The maximum number of issues loaded on the milestone overview page is 500.
 When the number exceeds the limit the page displays an alert and links to a paginated
 [issue list](../user/project/issues/managing_issues.md) of all issues in the milestone.
 
-- **Limit:** 3000 issues
+- **Limit:** 500 issues
 
 ## Number of pipelines per Git push