FE fix diffs specs leaking store

What does this MR do?

(CE Port: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/31698)

Throughout our spec/javascripts/spec we import the shared store rather than the store creator which causes some flakiness and non-determinism into these component tests 😱

• https://gitlab.com/gitlab-org/gitlab-ee/issues/13439
• https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/31694#note_202412274

This MR fixes this.