Only run unusedCompileDependenciesTest on the JVM

[rossabaker]

Should help with http4s/http4s#5926.

[armanbilge]

I'm not sure this will help us. The CI workflow is global to the whole build, not per-project.

What could help is if we added a conditional to this step that only runs if it is a JVM job. But this gets fiddly if we try and account for pure JVM (like the jdk client) or pure JS projects (like dom).

[armanbilge]

I know it doesn't help us right now, but what we should could do is absorb the explicit deps plugin into sbt-typelevel and apply this fix:

• Properly identify and check Scala.js dependencies cb372/sbt-explicit-dependencies#100

[armanbilge]

I have a fix incoming. Edit:

• Introduce Http4sOrgScalaJSPlugin #129

[rossabaker]

Oh, I thought this would run only on the JVM, but I did bake in an assumption everything was using cross project, which is probably not right.

[rossabaker]

#129 is better.