Update scala-compiler, scala-library, ... to 2.13.15

Author: scala-steward

build.sc

@@ -15,7 +15,7 @@ import de.tobiasroeser.mill.vcs.version.VcsVersion
 import com.github.lolgab.mill.mima._
 
 val scala212  = "2.12.18"
-val scala213  = "2.13.11"
+val scala213  = "2.13.15"
 
 val scala3   = "3.4.2"
 val scalaNative = "0.5.0"