chore: fixing build of test function

Author: Davide Melfi

experimental/aws-lambda-java-profiler/integration_tests/helloworld/build.gradle

@@ -1,11 +1,15 @@
-apply plugin: 'java'
+plugins {
+    id 'java'
+}
 
 repositories {
     mavenCentral()
 }
 
-sourceCompatibility = 21
-targetCompatibility = 21
+java {
+    sourceCompatibility = JavaVersion.VERSION_21
+    targetCompatibility = JavaVersion.VERSION_21
+}
 
 dependencies {
     implementation (