build(bulk-model-sync-gradle): set Java versions to 21 for test with …

…Gradle

The tests execute the Gradle build for modelix.core which requires Java 21.
Java 21 is required by the build for the Gradle plugin `dev.petuska.npm.publish`.

bulk-model-sync-gradle/build.gradle.kts

@@ -3,6 +3,14 @@ plugins {
     `java-gradle-plugin`
 }
 
+tasks.test {
+    javaLauncher.set(
+        javaToolchains.launcherFor {
+            languageVersion.set(JavaLanguageVersion.of(21))
+        },
+    )
+}
+
 dependencies {
     implementation(project(":model-client", "jvmRuntimeElements"))
     implementation(project(":bulk-model-sync-lib"))