Set explicit visibility of constant in NodaValidationHelper

src/NodaValidationHelper.php

@@ -11,7 +11,7 @@ declare(strict_types = 1);
  */
 final class NodaValidationHelper {
 
-    const ACTOR_DESCRIPTION_REQUIRED_DISTINCT_CHARS = 3;
+    private const ACTOR_DESCRIPTION_REQUIRED_DISTINCT_CHARS = 3;
 
     /**
      * Validates an actor description for completeness. Of course, only an informed