Fix test on Java 20

Checking console output content, likely a problem with the formatting
that makes the exact comparison fail.

Author: acogoluegnes

src/test/java/com/rabbitmq/stream/perf/StreamPerfTestTest.java

@@ -158,7 +158,9 @@ String consoleErrorOutput() {
   void helpShouldReturnImmediately() throws Exception {
     run(builder().help());
     waitRunEnds();
-    assertThat(consoleOutput()).contains("Usage: stream-perf-test");
+    assertThat(consoleOutput())
+        .contains("Display help information about the specified command")
+        .contains("stream-perf-test");
   }
 
   @Test