build: Upgrade to Jest 28 (#149)

I made the changes like this:

    npm install --save-dev --save-exact jest@28 @types/jest@28 ts-jest@28 jest-environment-jsdom@28

(`jest-environment-jsdom` [must be manually installed] in Jest 28.)

[must be manually installed]: https://jest-archive-august-2023.netlify.app/docs/28.x/upgrading-to-jest28/#jsdom