ISTWCMS-2220: Correct syntax error

run-tests.php

@@ -11,7 +11,7 @@ if (!$site_to_test || in_array($site_to_test, ['-h', '--help', '-v', '--version'
   echo 'Usage: ' . $script . " URL-TO-TEST [ADDITIONAL-ARGUMENTS ...]\n";
   echo "In Drupal 8, pass the argument --suppress-deprecations.\n";
   echo "(The argument is not needed for Drupal 9.)\n";
-  exit 1;
+  exit(1);
 }
 
 // Keep copy of original arguments to add to those set by this script.