phpstan fix

csp.install

@@ -92,7 +92,7 @@ function csp_update_20001(): ?TranslatableMarkup {
 /**
  * Update require-trusted-types-for config.
  */
-function csp_update_20201(): ?TranslatableMarkup {
+function csp_update_20201(): void {
   $config = \Drupal::configFactory()->getEditable('csp.settings');
 
   foreach (['enforce', 'report-only'] as $policyType) {
@@ -101,6 +101,4 @@ function csp_update_20201(): ?TranslatableMarkup {
       $config->save(TRUE);
     }
   }
-
-  return NULL;
 }