Add support for sbt 2

[OlegYch]

Currently fails with

   mkdir -p "$SBT_DOWNLOADPATH"
  curl -sL "https://github.com/sbt/sbt/releases/download/v$SBT_RUNNER_VERSION/sbt-$SBT_RUNNER_VERSION.zip" > \
    "$SBT_DOWNLOADPATH/sbt-$SBT_RUNNER_VERSION.zip"
  
  cd "$SBT_DOWNLOADPATH"
  unzip -o "sbt-$SBT_RUNNER_VERSION.zip" -d "$SBT_TOOLPATH"
  shell: /usr/bin/bash --noprofile --norc -e -o pipefail {0}
  env:
    JAVA_HOME: /opt/hostedtoolcache/Java_Adopt_jdk/11.0.26-4/x64
    JAVA_HOME_11_X64: /opt/hostedtoolcache/Java_Adopt_jdk/11.0.26-4/x64
    SBT_RUNNER_VERSION: 2.0.0-M4
    SBT_TOOLPATH: /opt/hostedtoolcache/sbt/2.0.0-M4
    SBT_DOWNLOADPATH: /home/runner/work/_temp/_sbt
  End-of-central-directory signature not found.  Either this file is not
  a zipfile, or it constitutes one disk of a multi-part archive.  In the
  latter case the central directory and zipfile comment will be found on
  the last disk(s) of this archive.
unzip:  cannot find zipfile directory in one of sbt-2.0.0-M4.zip or
        sbt-2.0.0-M4.zip.zip, and cannot find sbt-2.0.0-M4.zip.ZIP, period.
Archive:  sbt-2.0.0-M4.zip

[eed3si9n]

This is fine. I only release installer (runner + launcher + sbtn) under sbt 1.x. These can launch sbt 2.x.