Update scala-library to 2.12.20

Author: scala-steward

build.sbt

@@ -22,7 +22,7 @@ ThisBuild / developers       := List(
 // scala versions
 val scala3       = "3.3.3"
 val scala213     = "2.13.13"
-val scala212     = "2.12.19"
+val scala212     = "2.12.20"
 val defaultScala = scala3
 
 // github actions