Fix(Productivity Analytics): store initialization

Ensure export is an initialized store (singleton),
so multiple files can import the same store.

Issue introduced here:
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/41284/diffs#e78dbd127d4c8bfeb28a926d59a68fc64e92d90f_26_25

ee/app/assets/javascripts/analytics/productivity_analytics/store/index.js

@@ -22,4 +22,4 @@ export const getStoreConfig = () => ({
   },
 });
 
-export default () => new Vuex.Store(getStoreConfig());
+export default new Vuex.Store(getStoreConfig());

ee/changelogs/unreleased/255887-mlunoe-ensure-export-of-initialized-store.yml

+---
+title: Fixing an issue on the Productivity Analytics page, where applying filters
+  would not update the results. This should now work as expected; applying a filter
+  updates the results on the page filtered by the filters applied
+merge_request: 43532
+author:
+type: fixed

ee/spec/frontend/analytics/productivity_analytics/store/store_spec.js

+import store from 'ee/analytics/productivity_analytics/store';
+import state from 'ee/analytics/productivity_analytics/store/state';
+
+describe('Productivity analytics store', () => {
+  it('exports an initialized store', () => {
+    expect(store).toMatchObject({
+      state: state(),
+    });
+  });
+});