Fixed sidebar not collapsing on merge request in mobile screens

What does this MR do?

Fixes the issuable sidebar not collapsing on merge requests in mobile size screens

Why was this MR needed?

To fix an ongoing regression

Screenshots (if relevant)

Merge_Request_tab_not_showing_anymore

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

closes #32759 (closed)