Fix undefined epic issue path in epic tree

ee/app/assets/javascripts/related_items_tree/components/tree_item_body.vue

@@ -88,6 +88,9 @@ export default {
     itemId() {
       return this.itemReference.split(this.item.pathIdSeparator).pop();
     },
+    itemPath() {
+      return this.itemReference.split(this.item.pathIdSeparator)[0];
+    },
     itemHierarchy() {
       return this.itemPath + this.item.pathIdSeparator + this.itemId;
     },

ee/spec/frontend/related_items_tree/components/tree_item_body_spec.js

@@ -237,6 +237,12 @@ describe('RelatedItemsTree', () => {
         });
       });
 
+      describe('itemPath', () => {
+        it('returns string containing item path', () => {
+          expect(wrapper.vm.itemPath).toBe('gitlab-org/gitlab-shell');
+        });
+      });
+
       describe('computedPath', () => {
         it('returns value of `itemWebPath` when it is defined', () => {
           expect(wrapper.vm.computedPath).toBe(mockItem.webPath);
@@ -313,6 +319,7 @@ describe('RelatedItemsTree', () => {
         const path = itemPath + mockItem.pathIdSeparator + itemId;
 
         expect(stateTooltip.props('path')).toBe(path);
+        expect(path).toContain('gitlab-org/gitlab-shell');
       });
 
       it('renders confidential icon when `item.confidential` is true', () => {