Merge branch 'ee-36160-zindex' into 'master'

EE - Decreases z-index of select2 to a lower number of our navigation bar

See merge request gitlab-org/gitlab-ee!3175

app/assets/stylesheets/framework/selects.scss

@@ -61,6 +61,11 @@
   border: 1px solid $dropdown-border-color;
   min-width: 175px;
   color: $gl-text-color;
+  z-index: 999;
+}
+
+.select2-drop-mask {
+  z-index: 998;
 }
 
 .select2-drop.select2-drop-above.select2-drop-active {

changelogs/unreleased/36160-zindex.yml

+---
+title: Decreases z-index of select2 to a lower number of our navigation bar
+merge_request:
+author:
+type: fixed