Support absolute import paths in Jest

[fredrikekelund]

Related issues

• Follow-up to Allow non-relative imports starting with src/ or vendor/ #825

Proposed Changes

In #825, I added support for absolute imports starting with src/ or vendor/. Turns out we need to add this to Jest's config, too. This PR fixes that.

Testing Instructions

1. Change one of the relative import paths in src/components/content-tab-assistant.tsx to be absolute
2. Run npm run test src/components/tests/content-tab-assistant.test.tsx
3. Ensure that the tests pass

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[wojtekn]

Works as expected. The code change looks clear.