Stop scrollbar stretching filtered search box

Limit the height of the bordered box, so the scrollbar appears
outside of it rather than increasing its height.

app/assets/stylesheets/framework/filters.scss

@@ -265,6 +265,7 @@
   flex: 1;
   position: relative;
   min-width: 0;
+  height: 2rem;
   background-color: $input-bg;
 }
 

changelogs/unreleased/psi-boards-scrollbar.yml

+---
+title: Stop scrollbar stretching filtered search box
+merge_request: 54574
+author:
+type: fixed