Fix test detection in gradle

fmlloader-tests/build.gradle

@@ -11,4 +11,8 @@ dependencies {
     testImplementation(libs.guava)
     testImplementation(libs.junit.api)
     testRuntimeOnly(libs.bundles.junit.runtime)
+}
+
+tasks.named('test') {
+    useJUnitPlatform()
 }