Adds changes from @rayana and @annabeldunstone review

- Makes the callout close button a tertiary one
- Removes the monospaced font for branch dropdown results

app/assets/stylesheets/framework/typography.scss

@@ -665,7 +665,7 @@ code {
   font-size: 95%;
 }
 
-.git-revision-dropdown .dropdown-content ul li a {
+.git-revision-dropdown .dropdown-content li:not(.dropdown-menu-empty-item) a {
   font-family: $monospace-font;
   font-size: 95%;
   word-break: break-all;

app/views/admin/dev_ops_report/_callout.html.haml

 .gl-mt-3
 .user-callout{ data: { uid: 'dev_ops_report_intro_callout_dismissed' } }
   .bordered-box.landing.content-block
-    %button.gl-button.btn.btn-default.close.js-close-callout{ type: 'button',
+    %button.gl-button.btn.btn-default-tertiary.close.js-close-callout{ type: 'button',
       'aria-label' => _('Dismiss DevOps Report introduction') }
       = sprite_icon('close', size: 16, css_class: 'dismiss-icon')
     .user-callout-copy