Fix subgroup epic path on epic boards

Changelog: fixed
EE: true

ee/app/assets/javascripts/boards/components/epic_board_content_sidebar.vue

@@ -28,13 +28,16 @@ export default {
   inheritAttrs: false,
   computed: {
     ...mapGetters(['isSidebarOpen', 'activeBoardItem']),
-    ...mapState(['sidebarType', 'fullPath', 'issuableType']),
+    ...mapState(['sidebarType', 'issuableType']),
     isIssuableSidebar() {
       return this.sidebarType === ISSUABLE;
     },
     showSidebar() {
       return this.isIssuableSidebar && this.isSidebarOpen;
     },
+    fullPath() {
+      return this.activeBoardItem?.referencePath?.split('&')[0] || '';
+    },
   },
   methods: {
     ...mapActions(['toggleBoardItem', 'setActiveItemConfidential', 'setActiveItemSubscribed']),

ee/spec/frontend/boards/components/epic_board_content_sidebar_spec.js

@@ -87,8 +87,11 @@ describe('EpicBoardContentSidebar', () => {
     expect(wrapper.findComponent(GlDrawer).props('open')).toBe(true);
   });
 
-  it('renders SidebarTodoWidget', () => {
+  it('renders SidebarTodoWidget passing correct epic fullPath', () => {
     expect(wrapper.findComponent(SidebarTodoWidget).exists()).toBe(true);
+    expect(wrapper.findComponent(SidebarTodoWidget).props('fullPath')).toBe(
+      'gitlab-org/gitlab-subgroup',
+    );
   });
 
   it('renders BoardSidebarLabelsSelect', () => {

ee/spec/frontend/boards/mock_data.js

@@ -246,6 +246,7 @@ export const mockFormattedBoardEpic = {
   id: 41,
   iid: '1',
   title: 'Epic title',
+  referencePath: 'gitlab-org/gitlab-subgroup&41',
   state: 'opened',
   webUrl: '/groups/gitlab-org/-/epics/1',
   group: { fullPath: 'gitlab-org' },