Merge pull request #818 from typelevel/update/scala-library-2.12.21

Update scala-library to 2.12.21

Author: ahjohannessen

build.sbt

@@ -4,7 +4,7 @@ import Dependencies._
 
 lazy val Scala3 = "3.3.7"
 lazy val Scala213 = "2.13.18"
-lazy val Scala212 = "2.12.20"
+lazy val Scala212 = "2.12.21"
 
 lazy val axesDefault =
   Seq(VirtualAxis.scalaABIVersion(Scala213), VirtualAxis.jvm)