Merge pull request #339 from scala-steward/update/scala-library-2.12.21

Update scala-library to 2.12.21

Author: mkurz

build.sbt

@@ -7,7 +7,7 @@ startYear := Some(2011)
 homepage := scmInfo.value map (_.browseUrl)
 scmInfo := Some(ScmInfo(url("https://github.com/sbt/sbt-git"), "scm:git:[email protected]:sbt/sbt-git.git"))
 
-lazy val scala212 = "2.12.20"
+lazy val scala212 = "2.12.21"
 lazy val scala3 = "3.7.4"
 
 crossScalaVersions := Seq(scala212, scala3)