Fix KotlinCore

KotlinCore/build.gradle.kts

@@ -40,8 +40,8 @@ tasks.shadowJar {
 }
 
 java {
-    sourceCompatibility = JavaVersion.VERSION_17
-    targetCompatibility = JavaVersion.VERSION_17
+    sourceCompatibility = JavaVersion.VERSION_21
+    targetCompatibility = JavaVersion.VERSION_21
 }
 
 sourceSets {
@@ -63,5 +63,5 @@ dependencies {
 }
 
 kotlin {
-    jvmToolchain(17)
+    jvmToolchain(21)
 }