MR sidebar toggle button position fix

Changelog: fixed

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

@@ -14,7 +14,7 @@
 
   .detail-page-header.border-bottom-0.gl-display-block.gl-pt-5{ class: "gl-md-display-flex! #{'is-merge-request' if moved_mr_sidebar_enabled? && !fluid_layout}" }
     .detail-page-header-body
-      %h1.title.page-title.gl-font-size-h-display.gl-my-0.gl-display-inline-block{ data: { testid: 'title-content' } }
+      %h1.title.page-title.gl-font-size-h-display.gl-my-0.gl-display-inline-block.gl-flex-grow-1{ data: { testid: 'title-content' } }
         = markdown_field(@merge_request, :title)
 
       - unless hide_gutter_toggle