Run scala2-compat scripted tests during test_bootstrapped in CI

[griggt]

This PR adds the Scala 2 compatibility/interop tests to the test_bootstrapped job in CI. The status quo is that these tests are only run during the nightly scheduled CI (as part of test_sbt).

Adding the tests to the test_bootstrapped job means any regressions are noticed sooner, and CI configuration overrides should not be needed when fixing Scala 2 interop issues such as #9916.

The tests are currently implemented as sbt scripted tests, which have a high per-test startup overhead, but the number of tests is small so the overall impact on CI runtime should be minimal (1-2 minutes).

An alternative to #9990.

[dottybot]

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[smarter]

First, congrats on getting PR #10000 🥳!

The tests are currently implemented as sbt scripted tests, which have a high per-test startup overhead, but the number of tests is small so the overall impact on CI runtime should be minimal (1-2 minutes).

It's fine for now, but if we end up adding more tests we should either merge them together in one sbt project or finally make our testing framework capable of calling scalac for specific files and use that instead.

[griggt]

if we end up adding more tests we should either merge them together in one sbt project or finally make our testing framework capable of calling scalac for specific files and use that instead.

Agreed. I hope to find some time soon to do some work on the latter.