Update kotlin monorepo to v2.3.21

Author: renovate[bot]

build.sbt

@@ -24,7 +24,7 @@ lazy val V =
     val requests = "0.8.0"
     val minimalMillVersion = "0.10.0"
     val millScipVersion = "0.3.6"
-    val kotlinVersion = "2.1.20"
+    val kotlinVersion = "2.3.21"
   }
 
 inThisBuild(