Update scala-library to 2.12.20

Author: scala-steward-bot

build.sbt

@@ -3,7 +3,7 @@ ThisBuild / organization := "com.github.sbt"
 lazy val protobuf = "com.google.protobuf" % "protobuf-java" % "3.25.4" % Runtime // for scala-steward
 lazy val grpc = "io.grpc" % "protoc-gen-grpc-java" % "1.62.2" % Runtime // for scala-steward
 
-def scala212 = "2.12.19"
+def scala212 = "2.12.20"
 
 lazy val root = (project in file("."))
   .enablePlugins(SbtPlugin)