Add JUnit dependencies to Java modules

Not really used for anything yet, but Gradle moans because
xtea-plugin/src/test/ exists and it can't find the JUnit engine.

Signed-off-by: Graham <gpe@openrs2.org>

build.gradle.kts

@@ -110,6 +110,17 @@ configure(subprojects.filter { it.isFree }) {
         toolVersion = "0.8.7"
     }
 
+    plugins.withType<JavaPlugin> {
+        dependencies {
+            val testImplementation by configurations
+            testImplementation(libs.junit.api)
+
+            val testRuntimeOnly by configurations
+            testRuntimeOnly(libs.junit.engine)
+            testRuntimeOnly(libs.junit.launcher)
+        }
+    }
+
     plugins.withType<KotlinPluginWrapper> {
         apply(plugin = "org.jetbrains.dokka")
         apply(plugin = "org.jmailen.kotlinter")