Update sbt-scalajs, scalajs-compiler, ... to 1.20.1 (#679)

Co-authored-by: typelevel-steward[bot] <106827141+typelevel-steward[bot]@users.noreply.github.com>
Co-authored-by: Filipe Regadas <oss@regadas.email>

Author: typelevel-steward[bot]

project/plugins.sbt

@@ -1,6 +1,6 @@
 addSbtPlugin("org.portable-scala" % "sbt-scala-native-crossproject" % "1.3.2")
 addSbtPlugin("org.scala-native" % "sbt-scala-native" % "0.5.9")
-addSbtPlugin("org.scala-js" % "sbt-scalajs" % "1.18.2")
+addSbtPlugin("org.scala-js" % "sbt-scalajs" % "1.20.1")
 addSbtPlugin("org.scoverage" % "sbt-scoverage" % "2.4.2")
 addSbtPlugin("pl.project13.scala" % "sbt-jmh" % "0.4.8")
 addSbtPlugin("org.typelevel" % "sbt-typelevel" % "0.8.2")