MINOR: fix error message in TestRaftServer.scala (#9812)

Reviewers: Chia-Ping Tsai <chia7712@gmail.com>

core/src/main/scala/kafka/tools/TestRaftServer.scala

@@ -618,7 +618,7 @@ object TestRaftServer extends Logging {
       case e: OptionException =>
         CommandLineUtils.printUsageAndDie(opts.parser, e.getMessage)
       case e: Throwable =>
-        fatal("Exiting Kafka due to fatal exception", e)
+        fatal("Exiting raft server due to fatal exception", e)
         Exit.exit(1)
     }
   }