test: make spawn_helper4 never return

Its whole raison d'être is to sleep until it's killed.

test/run-tests.c

@@ -70,8 +70,8 @@ static int maybe_run_test(int argc, char **argv) {
   }
 
   if (strcmp(argv[1], "spawn_helper4") == 0) {
-    uv_sleep(10000);
-    return 1;
+    /* Never surrender, never return! */
+    while (1) uv_sleep(10000);
   }
 
   return run_test(argv[1], TEST_TIMEOUT, 0);