fix: Missing kotlin compiler config (#9755)

Author: bric3

dd-java-agent/agent-ci-visibility/build.gradle

@@ -1,4 +1,6 @@
 import com.github.jengelman.gradle.plugins.shadow.tasks.ShadowJar
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+import org.jetbrains.kotlin.gradle.dsl.KotlinVersion
 
 plugins {
   id 'com.gradleup.shadow'
@@ -53,3 +55,11 @@ tasks.named("compileTestGroovy") {
     " otherwise anonymous class has one `loadClass` accessor's signature has `java.lang.Module`"
     )
 }
+
+kotlin {
+  compilerOptions {
+    jvmTarget = JvmTarget.JVM_1_8
+    apiVersion = KotlinVersion.KOTLIN_1_6
+    languageVersion = KotlinVersion.KOTLIN_1_6
+  }
+}