Change assignee in mr list to use gl-class

Issue: https://gitlab.com/gitlab-org/gitlab/-/issues/259607

This will make it match reviewers

app/views/projects/merge_requests/_merge_request.html.haml

@@ -53,7 +53,7 @@
             = link_to merge_request_path(merge_request), class: "has-tooltip", title: _('Cannot be merged automatically') do
               = sprite_icon('warning-solid')
         - if merge_request.assignees.any?
-          %li.d-flex
+          %li.gl-display-flex
             = render 'shared/issuable/assignees', project: merge_request.project, issuable: merge_request
         = render 'projects/merge_requests/approvals_count', merge_request: merge_request