modal: fix record adding to a community

* closes #2821

invenio_app_rdm/theme/assets/semantic-ui/js/invenio_app_rdm/landing_page/RecordCommunitySubmission/RecordCommunitySubmissionModal.js

@@ -79,7 +79,14 @@ export class RecordCommunitySubmissionModal extends Component {
           ],
         };
       }
-      const response = await http.post(recordCommunityEndpoint, data);
+      // When adding communities to a record, it should simple return the json representation of the response
+      // no need to process the response with the schema serializer
+      const response = await http.post(recordCommunityEndpoint, data, {
+        headers: {
+          "Accept": "application/json",
+          "Content-Type": "application/json",
+        },
+      });
       this.handleSuccessSubmit(response.data);
     } catch (error) {
       console.error(error);