test: initialize project groups in worktree slice fixture

src/renderer/src/store/slices/worktrees/worktrees-slice-test-harness.ts

@@ -153,6 +153,7 @@ export function createTestStore() {
           ]
         ]),
         repos: [],
+        projectGroups: [],
         projectHostSetups: [],
         deleteProjectHostSetup: vi.fn().mockResolvedValue(null),
         updateFolderWorkspace: vi.fn().mockResolvedValue(true),