Resolve "Ankündigungen: Layout-Fehler bei den Dropdowns im Dialog"

Closes #1363

Merge request studip/studip!1049

resources/assets/stylesheets/less/quicksearch.less

@@ -101,14 +101,13 @@ div.quicksearch_frame {
         overflow: visible;
         position: relative;
         top: 31px;
+        z-index: 99999;
 
         .autocomplete__results {
             list-style-type: none;
             padding: 1px;
             border: 1px solid @light-gray-color-40;
             background-color: white;
-            z-index: 99999;
-            width: 200px;
             max-height: 275px;
             width: 600px;
             overflow-x: auto;