Fix bug in testing by class

If --class is the first parameter, array_search() will return zero,
which is interpreted as it not having been found.

Fixes issue introduced in 86bf0772.

run-tests.php

@@ -38,7 +38,7 @@ $_SERVER['argv'] = [
   $site_to_test,
 ];
 // Allow testing specified classes. Default to running all module tests.
-if (!array_search('--class', $original_argv)) {
+if (!in_array('--class', $original_argv)) {
   $_SERVER['argv'][] = '--module';
   $_SERVER['argv'][] = implode(',', $modules_to_test);
 }