fix(tests): increase sleep duration in shows_history_message test for improved timing

tests/functionaltests/test_muc.c

@@ -146,7 +146,7 @@ shows_history_message(void **state)
             "<x xmlns='jabber:x:delay' stamp='20151219T23:55:25'/>"
         "</message>"
     );
-    sleep(1);
+    sleep(2);
 
     assert_true(prof_output_regex("testoccupant:.*an old message"));
 }