Cross build for sbt 2.0.0-M4

[mrdziuban]

The only thing blocking this is that Def.inputTaskDyn doesn't exist. It was added in sbt/sbt#8033 but hasn't been released yet.

New blocker after upgrading to sbt 2.0.0-M4 is this error in the tests:

-- [E172] Type Error: /Users/matt/sbt-dependency-submission/sbt-plugin/src/test/scala/ch/epfl/scala/JsonProtocolTests.scala:16:45
16 |    val obtained = Converter.toJson(metadata).get
   |                                             ^
   |Cannot find JsonWriter or JsonFormat type class for Map[String, sjsonnew.shaded.scalajson.ast.unsafe.JValue].
   |I found:
   |
   |    ch.epfl.scala.githubapi.JsonProtocol.mapFormat[String,
   |      sjsonnew.shaded.scalajson.ast.unsafe.JValue](
   |      ch.epfl.scala.githubapi.JsonProtocol.StringJsonKeyFormat,
   |      ch.epfl.scala.githubapi.JsonProtocol.isoStringLongFormat[
   |        sjsonnew.shaded.scalajson.ast.unsafe.JValue](
   |        /* missing */
   |          summon[sjsonnew.IsoStringLong[sjsonnew.shaded.scalajson.ast.unsafe.JValue]
   |            ]
   |      )
   |    )
   |
   |But no implicit values were found that match type sjsonnew.IsoStringLong[sjsonnew.shaded.scalajson.ast.unsafe.JValue].

[adpi2]

Thanks for working on the migration to sbt 2.x. It looks good so far.

[mrdziuban]

@adpi2 the main sources are compiling with sbt 2.0.0-M4 now but the tests won't compile, there are a couple compile errors about finding JsonFormat/JsonWriter instances. I put one in the description of the PR -- do you have any idea how to resolve it?