Fix build with java 20

- previous fix required a jdk 17 to be installed as well

buildSrc/build.gradle.kts

@@ -1,11 +1,17 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+import org.jetbrains.kotlin.gradle.dsl.KotlinJvmCompilerOptions
+import org.jetbrains.kotlin.gradle.tasks.KotlinCompilationTask
+
 plugins {
     `kotlin-dsl`
 }
 
-kotlin {
-    jvmToolchain {
-        languageVersion.set(JavaLanguageVersion.of("17"))
+tasks.named<KotlinCompilationTask<KotlinJvmCompilerOptions>>("compileKotlin").configure {
+    compilerOptions.jvmTarget.set(JvmTarget.JVM_17)
 }
+
+java {
+    targetCompatibility = JavaVersion.VERSION_17
 }
 
 repositories {