Fix lint errors (except @typescript-eslint/prefer-nullish-coalescing) (#9311)

* `yarn workspace client run lint --fix`

* `eslint-disable-next-line no-var` for service worker self

* A few more manual sw fixes

* word change

packages/sw/src/scripts/lang.ts

@@ -1,8 +1,6 @@
 /*
  * Language manager for SW
  */
-declare var self: ServiceWorkerGlobalScope;
-
 import { get, set } from 'idb-keyval';
 import { I18n } from '@/scripts/i18n';