Update scala-library to 2.13.15

Author: scala-steward

build.sbt

@@ -29,7 +29,7 @@ val scalac212Opts = baseScalaOpts ++ Seq("-Ypartial-unification")
 
 lazy val global = {
   Seq(
-    scalaVersion  := "2.13.10",
+    scalaVersion  := "2.13.15",
     organization  := "com.fullfacing",
     scalacOptions ++= (CrossVersion.partialVersion(scalaVersion.value) match {
       case Some((2, n)) if n <= 12 => scalac212Opts