[jena5] UI e2e tests have a 404 to `/` which appears to stop tests

### Change

As per title, running `yarn test:e2e` isn't working properly. The tests should pass as manual tests passed fine. But there are requests to `/` returning `404` in the fake backend. I think some configuration settings in Cypress or json-server changed and are causing this issue.

### Are you interested in contributing a pull request for this task?

Yes

Start by running `yarn test:e2e` and inspect the Cypress and json-server configuration mentioned in the issue. Trace the requests to `/` in the fake backend; the work is done when the UI end-to-end tests run successfully without the 404 responses stopping them.

Written by the indexing model from the issue text.