Compile with Scala 3

[fthomas]

[fthomas]

The Scala 3 build fails with:

[info] compiling 141 Scala sources to /home/runner/work/scala-steward/scala-steward/modules/core/.jvm/target/scala-3.0.0-RC2/classes ...
exception caught when loading trait GenConcurrent: java.lang.AssertionError: assertion failed: duplicate type F#45910; previous was type F#45561
[info] assertion failure for org.scalasteward.core.application.Context.type <:< ?{ step0: ? }, frozen = false
[info] exception occurred while typechecking /home/runner/work/scala-steward/scala-steward/modules/core/src/main/scala/org/scalasteward/core/Main.scala

It seems we're hitting https://github.com/lampepfl/dotty/issues/11173 here.

[fthomas]

The following dependencies are currently not available for Scala 3:

• io.circe:circe-generic-extras_3:0.14.3: https://github.com/circe/circe-generic-extras/issues/168
• io.get-coursier:coursier-sbt-maven-repository_3:2.1.8: https://github.com/coursier/coursier/issues/2001