build: Set target bytecode level to JVM 11

build.gradle.kts

@@ -1,4 +1,5 @@
 import org.gradle.kotlin.dsl.support.listFilesOrdered
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
 
 plugins {
     alias(libs.plugins.kotlin)
@@ -29,7 +30,13 @@ dependencies {
 }
 
 kotlin {
-    jvmToolchain(11)
+    compilerOptions {
+        jvmTarget.set(JvmTarget.JVM_11)
+    }
+}
+
+java {
+    targetCompatibility = JavaVersion.VERSION_11
 }
 
 tasks {