Manually load sinon and chai

karma-sinon-chai is not compatible with Chai 5+, and Karma is no longer
being updated.

Load sinon and chai manually instead, until we can have a long term plan
in place.

tests/test.localization.js

@@ -1,4 +1,3 @@
-const expect = chai.expect;
 import _, { Localizer, l10n } from '../app/localization.js';
 
 describe('Localization', function () {