Default to a Scala version for REPL if there are no Scala artifacts.

[trilleplay]

Solves #2430

Currently if there's only non-scala artifacts available when launching the REPL, it throws an error because the underlying logic relied on there being at least one Scala artifact available. This commit resolves the latest version available if we're unable to infer a version from a Scala artifact.

This is my first commit to the project, I've had a look at the contributing document as best as I could but do let me know if I'm missing something!

[MaciejG604]

Hello @trilleplay, thank you for the contribution!

The fix seems to be enough, but to make sure we should have it tested.
Could you add a test case covering the issue to modules/integration/src/test/scala/scala/cli/integration/ReplTests.scala?
You can take inspiration from modules/integration/src/test/scala/scala/cli/integration/RunTestDefinitions.scala.

a command for running the ReplTests will be:

./mill integration.test.jvm 'scala.cli.integration.ReplTests.*'

More info on this in DEV.md

[trilleplay]

Hey @MaciejG604 , I've gone ahead and introduced a test for this in my latest commit!

[MaciejG604]

Looks good, thanks for helping!