community-build: less noisy output

- Turn off sbt supershell, it leaves junk in the output.
- Turn off all warnings, no one is going to fix them anyway.

Author: smarter

community-build/test/scala/dotty/communitybuild/CommunityBuildTest.scala

@@ -95,15 +95,15 @@ final case class SbtCommunityProject(
     dependencies: List[CommunityProject] = Nil,
     sbtPublishCommand: String = null) extends CommunityProject:
   override val binaryName: String = "sbt"
-  private val baseCommand = s";clean ;set updateOptions in Global ~= (_.withLatestSnapshots(false)) ;++$compilerVersion! "
+  private val baseCommand = s";clean ;set logLevel in Global := Level.Error ;set updateOptions in Global ~= (_.withLatestSnapshots(false)) ;++$compilerVersion! "
   override val testCommand = s"$baseCommand$sbtTestCommand"
   override val updateCommand = s"$baseCommand$sbtUpdateCommand"
   override val publishCommand = s"$baseCommand$sbtPublishCommand"
 
   override val runCommandsArgs: List[String] =
     // Run the sbt command with the compiler version and sbt plugin set in the build
     val sbtProps = Option(System.getProperty("sbt.ivy.home")) match
-      case Some(ivyHome) => List(s"-Dsbt.ivy.home=$ivyHome")
+      case Some(ivyHome) => List(s"-Dsbt.ivy.home=$ivyHome", "-Dsbt.supershell=false")
       case _ => Nil
     extraSbtArgs ++ sbtProps ++ List(
       "-sbt-version", "1.3.8",