Removes EE differences for modal issues board

app/assets/javascripts/boards/components/modal/footer.vue

 <script>
+import footerEEMixin from 'ee_else_ce/boards/mixins/modal_footer';
 import Flash from '../../../flash';
 import { __, n__ } from '../../../locale';
 import ListsDropdown from './lists_dropdown.vue';
@@ -10,7 +11,7 @@ export default {
   components: {
     ListsDropdown,
   },
-  mixins: [modalMixin],
+  mixins: [modalMixin, footerEEMixin],
   data() {
     return {
       modal: ModalStore.store,

app/assets/javascripts/boards/mixins/modal_footer.js

+export default {};