Update sbt-scalajs, scalajs-compiler, ... to 1.21.0

Author: typelevel-steward[bot]

project/plugins.sbt

@@ -1,7 +1,7 @@
 val sbtTypelevelVersion = "0.8.5"
 addSbtPlugin("org.typelevel" % "sbt-typelevel" % sbtTypelevelVersion)
 addSbtPlugin("org.typelevel" % "sbt-typelevel-site" % sbtTypelevelVersion)
-addSbtPlugin("org.scala-js" % "sbt-scalajs" % "1.20.2")
+addSbtPlugin("org.scala-js" % "sbt-scalajs" % "1.21.0")
 addSbtPlugin("org.scala-native" % "sbt-scala-native" % "0.5.10")
 addSbtPlugin("com.armanbilge" % "sbt-scala-native-config-brew-github-actions" % "0.4.0")
 addSbtPlugin("io.github.sbt-doctest" % "sbt-doctest" % "0.12.4")