Do not show "Create merge request" button on issues when merge requests are disabled

When merge requests are disabled, in legacy issues the "Create merge request" button is replaced with a "Create branch" button. We need to update work item issues with the same behaviour.

legacy issues work item issues
user_creates_branch_and_merge_request_on_issue_page_when_signed_in_when_merge_requests_are_disabled_ user_creates_branch_and_merge_request_on_issue_page_when_signed_in_when_merge_requests_are_disabled__2
Edited by 🤖 GitLab Bot 🤖