Pass the iid of the User List on Update

The IID is needed to calculate the API endpoint to request when
updating the user list.

ee/app/assets/javascripts/user_lists/store/edit/actions.js

@@ -14,6 +14,7 @@ export const dismissErrorAlert = ({ commit }) => commit(types.DISMISS_ERROR_ALER
 
 export const updateUserList = ({ commit, state }, userList) => {
   return Api.updateFeatureFlagUserList(state.projectId, {
+    iid: userList.iid,
     name: userList.name,
   })
     .then(({ data }) => redirectTo(data.path))

ee/changelogs/unreleased/fix-update-user-list-404.yml

+---
+title: Pass the IID of the User List on Update
+merge_request: 39639
+author:
+type: fixed

ee/spec/frontend/user_lists/components/edit_user_list_spec.js

@@ -111,6 +111,7 @@ describe('ee/user_lists/components/edit_user_list', () => {
       it('should create a user list with the entered name', () => {
         expect(Api.updateFeatureFlagUserList).toHaveBeenCalledWith('1', {
           name: 'test',
+          iid: userList.iid,
         });
       });
 

ee/spec/frontend/user_lists/store/edit/actions_spec.js

@@ -87,6 +87,7 @@ describe('User Lists Edit Actions', () => {
         return testAction(actions.updateUserList, updatedList, state, [], [], () => {
           expect(Api.updateFeatureFlagUserList).toHaveBeenCalledWith('1', {
             name: updatedList.name,
+            iid: updatedList.iid,
           });
           expect(redirectTo).toHaveBeenCalledWith(userList.path);
         });
@@ -111,6 +112,7 @@ describe('User Lists Edit Actions', () => {
           () =>
             expect(Api.updateFeatureFlagUserList).toHaveBeenCalledWith('1', {
               name: updatedList.name,
+              iid: updatedList.iid,
             }),
         );
       });