Make Fail Overflow Test less flaky

Fail overflow test can fail to pass if exception is thrown after more then 256 messages have been processed

#162

tck/src/main/java/org/eclipse/microprofile/reactive/messaging/tck/channel/overflow/FailOverflowStrategyOverflowTest.java

@@ -45,7 +45,7 @@ public void testOverflow() {
 
         await().until(() -> bean.exception() != null);
         assertThat(bean.output()).doesNotContain("999");
-        assertThat(bean.output()).hasSizeBetween(0, 256);
+        assertThat(bean.output()).isNotEmpty().hasSizeLessThan(999);
         assertThat(bean.failure()).isNotNull().isInstanceOf(Exception.class);
     }
 }