incidents in legacy issue view have overlapping content when work item FF enabled and new issue look is toggled on

Originally reported: https://gitlab.com/gitlab-org/gitlab/-/issues/512715#note_2339770203

In some cases, when work_items_view_preference is enabled for a user, and work item view is toggled "On", users are seeing content spanning the entire legacy issue page including behind the sidebar. This seems to only affect incidents.

This has been reported on the following, which are both incidents:

• gitlab-com/gl-infra/production#19229 (closed)
• gitlab-org/quality/engineering-productivity/master-broken-incidents#10402 (closed)