Update to latest enketo-core

[jkuester]

Now that we are done with #7599, it seems like a good idea to start preparing for updating to the next Enekto version! 😆

As @m5r pointed out on Slack, the enketo-core repo has been moved into the big Enketo monorepo: https://github.com/enketo/enketo/blob/main/packages/enketo-core and version 8.0.0 has been released:

• Breaking change: in the move to a monorepo, some paths in Sass styles have been updated to reflect the new file structure. The impact should be minimal, but custom themes may need to be updated. Generally, paths which cross package boundaries (i.e. imports from Enketo Express to styles in Enketo Core, or imports of third party styles from NPM packages) should use absolute paths from the monorepo root. You may refer to existing theme styles for examples.
• Breaking change: Support Node 18 and 20, drop support for older versions

It may make sense to try to address this issue at the same time: #8741