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

Author: typelevel-steward[bot]

project/plugins.sbt

@@ -2,6 +2,6 @@ val sbtTlVersion = "0.7.7"
 addSbtPlugin("org.typelevel" % "sbt-typelevel" % sbtTlVersion)
 addSbtPlugin("org.typelevel" % "sbt-typelevel-mergify" % sbtTlVersion)
 addSbtPlugin("org.typelevel" % "sbt-typelevel-site" % sbtTlVersion)
-addSbtPlugin("org.scala-js" % "sbt-scalajs" % "1.17.0")
+addSbtPlugin("org.scala-js" % "sbt-scalajs" % "1.21.0")
 addSbtPlugin("org.scala-native" % "sbt-scala-native" % "0.4.17")
 addSbtPlugin("com.eed3si9n" % "sbt-buildinfo" % "0.13.1")