Fix tag rendering error in hashtag column settings (#17184)

* Flatten tags in configuration to regular array before converting to JSON

* Render filter tags using toJS instead of toJSON

app/javascript/mastodon/features/hashtag_timeline/components/column_settings.js

@@ -33,8 +33,8 @@ class ColumnSettings extends React.PureComponent {
   tags (mode) {
     let tags = this.props.settings.getIn(['tags', mode]) || [];
 
-    if (tags.toJSON) {
+    if (tags.toJS) {
-      return tags.toJSON();
+      return tags.toJS();
     } else {
       return tags;
     }