Add comment about not using earlier versions

Author: aaron-ai

instrumentation/rocketmq/rocketmq-client/rocketmq-client-java-5.0/testing/build.gradle.kts

@@ -5,6 +5,7 @@ plugins {
 dependencies {
   api(project(":testing-common"))
 
+  // earlier versions have bugs that may make tests flaky.
   implementation("org.apache.rocketmq:rocketmq-client-java:5.0.2")
   implementation("org.testcontainers:testcontainers:1.17.5")
   implementation("io.opentelemetry:opentelemetry-api")