Fix gl_dropdown scrolling to top on assignee click

**How?**
It looks like when assignees are clicked, the child of the `<a>`.
We fix our propogation check by looking at `.closest` which traverses
through the element itself and parent.

app/assets/javascripts/gl_dropdown.js

@@ -567,7 +567,7 @@ GitLabDropdown = (function() {
         e.stopPropagation();
 
         // This prevents automatic scrolling to the top
-        if ($target.is('a')) {
+        if ($target.closest('a').length) {
           return false;
         }
       }

changelogs/unreleased/fe-fix-gl-dropdown-scrolling-to-top.yml

@@ -0,0 +1,5 @@
+---
+title: Fix scrolling to top on assignee change
+merge_request: 29500
+author:
+type: fixed