Bump preferred Kotlin version to 2.1.0

Author: gesellix

engine/build.gradle.kts

@@ -61,7 +61,7 @@ dependencies {
       implementation(it) {
         version {
           strictly("[1.6,3)")
-          prefer("2.0.20")
+          prefer("2.1.0")
         }
       }
     }

integrationtest/build.gradle.kts

@@ -50,7 +50,7 @@ dependencies {
       implementation(it) {
         version {
           strictly("[1.6,3)")
-          prefer("2.0.20")
+          prefer("2.1.0")
         }
       }
     }