Prevent weightSum to be updated on child epic fetch

`weightSum` should not be updated when child subepic was
fetched

EE: true
Changelog: fixed

ee/app/assets/javascripts/related_items_tree/store/actions.js

@@ -124,9 +124,8 @@ export const fetchItems = ({ dispatch }, { parentItem, isSubItem = false }) => {
         pageInfo: data.group.epic.issues.pageInfo,
       });
 
-      dispatch('setWeightSum', data.group.epic.descendantWeightSum);
-
       if (!isSubItem) {
+        dispatch('setWeightSum', data.group.epic.descendantWeightSum);
         dispatch('setChildrenCount', data.group.epic.descendantCounts);
         dispatch('setHealthStatus', data.group.epic.healthStatus);
       }

ee/spec/frontend/related_items_tree/store/actions_spec.js

@@ -448,6 +448,71 @@ describe('RelatedItemTree', () => {
           );
         });
 
+        it('should not dispatch `setWeightSum`, `setChildrenCount`, `setHealthStatus` when isSubItem is true', () => {
+          jest.spyOn(epicUtils.gqClient, 'query').mockReturnValue(
+            Promise.resolve({
+              data: mockQueryResponse.data,
+            }),
+          );
+
+          const children = epicUtils.processQueryResponse(mockQueryResponse.data.group);
+
+          const {
+            children: { pageInfo: epicPageInfo },
+            issues: { pageInfo: issuesPageInfo },
+          } = mockQueryResponse.data.group.epic;
+
+          testAction(
+            actions.fetchItems,
+            { parentItem: mockParentItem, isSubItem: true },
+            {},
+            [],
+            [
+              {
+                type: 'requestItems',
+                payload: { parentItem: mockParentItem, isSubItem: true },
+              },
+              {
+                type: 'receiveItemsSuccess',
+                payload: {
+                  parentItem: mockParentItem,
+                  isSubItem: true,
+                  children,
+                },
+              },
+              {
+                type: 'setItemChildren',
+                payload: {
+                  parentItem: mockParentItem,
+                  isSubItem: true,
+                  children,
+                },
+              },
+              {
+                type: 'setItemChildrenFlags',
+                payload: {
+                  isSubItem: true,
+                  children,
+                },
+              },
+              {
+                type: 'setEpicPageInfo',
+                payload: {
+                  parentItem: mockParentItem,
+                  pageInfo: epicPageInfo,
+                },
+              },
+              {
+                type: 'setIssuePageInfo',
+                payload: {
+                  parentItem: mockParentItem,
+                  pageInfo: issuesPageInfo,
+                },
+              },
+            ],
+          );
+        });
+
         it('should dispatch `receiveItemsFailure` on request failure', () => {
           jest.spyOn(epicUtils.gqClient, 'query').mockReturnValue(Promise.reject());