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

Author: scala-steward

project/plugins.sbt

@@ -1,6 +1,6 @@
 addSbtPlugin("com.github.sbt"     % "sbt-ci-release"           % "1.5.12")
 addSbtPlugin("com.typesafe"       % "sbt-mima-plugin"          % "1.1.3")
-addSbtPlugin("org.scala-js"       % "sbt-scalajs"              % "1.16.0")
+addSbtPlugin("org.scala-js"       % "sbt-scalajs"              % "1.21.0")
 addSbtPlugin("org.portable-scala" % "sbt-scalajs-crossproject" % "1.3.2")
 addSbtPlugin("org.scala-js"       % "sbt-jsdependencies"       % "1.0.2")
 addSbtPlugin("io.get-coursier"    % "sbt-shading"              % "2.1.4")