fix: pin JVM toolchain to version 21 and simplify test JVM arguments

Author: ksqeib

auth-yggd/build.gradle.kts

@@ -49,13 +49,8 @@ dependencies {
 
 tasks.test {
     useJUnitPlatform()
-    val currentJavaMajor = JavaVersion.current().majorVersion.toIntOrNull() ?: 0
-    if (currentJavaMajor >= 21) {
-        jvmArgs("--enable-native-access=ALL-UNNAMED")
-    }
-    if (currentJavaMajor >= 24) {
-        jvmArgs("--sun-misc-unsafe-memory-access=allow")
-    }
+    // JVM toolchain is pinned to 21; --enable-native-access is supported from Java 21 onwards.
+    jvmArgs("--enable-native-access=ALL-UNNAMED")
     testLogging {
         showStandardStreams = false
     }

build.gradle.kts

@@ -206,6 +206,12 @@ subprojects {
     group = rootProject.group
     version = rootProject.version
 
+    plugins.withId("org.jetbrains.kotlin.jvm") {
+        extensions.configure<org.jetbrains.kotlin.gradle.dsl.KotlinJvmProjectExtension> {
+            jvmToolchain(21)
+        }
+    }
+
     repositories {
         maven("https://maven.aliyun.com/repository/central")
         maven("https://mirrors.cloud.tencent.com/nexus/repository/maven-public/")