Update sbt-scalajs, scalajs-compiler, ... to 1.20.1

Author: typelevel-steward[bot]

project/plugins.sbt

@@ -1,4 +1,4 @@
-addSbtPlugin("org.scala-js" % "sbt-scalajs" % "1.18.2")
+addSbtPlugin("org.scala-js" % "sbt-scalajs" % "1.20.1")
 addSbtPlugin("org.typelevel" % "sbt-typelevel" % "0.8.2")
 addSbtPlugin("org.scala-native" % "sbt-scala-native" % "0.5.9")
 addSbtPlugin("org.portable-scala" % "sbt-scala-native-crossproject" % "1.3.2")