Migrate legacy diffs getters spec to pinia
requested to merge slashmanov/migrate-legacy-diffs-getters-spec-to-pinia into slashmanov/migrate-legacy-diffs-actions-spec-to-pinia
What does this MR do and why?
This MR migrates copied Vuex diffs app getters spec to Pinia.
Part of Migrate Diffs and Notes Vuex stores to Pinia (#474653).