Cleanup aria tag handling added in StatelessTags.

See comments at https://github.com/galaxyproject/galaxy/pull/16159#discussion_r1210464678

client/src/components/TagsMultiselect/StatelessTags.vue

@@ -63,12 +63,10 @@ const editing = ref(false);
 
 function onOpen() {
     editing.value = true;
-    multiselectElement.value?.$el.setAttribute("aria-expanded", "true");
 }
 
 function onClose() {
     editing.value = false;
-    multiselectElement.value?.$el.setAttribute("aria-expanded", "false");
 }
 
 const multiselectElement: Ref<Multiselect | null> = ref(null);
@@ -126,7 +124,7 @@ function onTagClicked(tag: string) {
             :multiple="true"
             :taggable="true"
             :close-on-select="false"
-            aria-expanded="false"
+            :aria-expanded="editing ? 'true' : 'false'"
             @tag="onAddTag"
             @input="onInput"
             @open="onOpen"