[Glitch] Fix media uploads in composer appearing over search results in advanced interface

Port b5006539c9 to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/flavours/glitch/styles/components.scss

@@ -3793,6 +3793,7 @@ $ui-header-logo-wordmark-width: 99px;
   overflow-y: auto;
   width: 100%;
   height: 100%;
+  z-index: 0;
 }
 
 .drawer__inner__mastodon {