Fixed regression for dropdowns

Limited the custom styling of anchors in dropdowns to direct children of
<li> so that it doesn't affect potential anchors deeper in items'
structure (see https://gitlab.com/gitlab-org/gitlab/issues/35834)

app/assets/stylesheets/framework/dropdowns.scss

@@ -288,7 +288,7 @@
     list-style: none;
     padding: 0 1px;
 
-    a:not(.help-link),
+    > a,
     button,
     .menu-item {
       @include dropdown-link;