title: Yii2 validation rule in model have multiple scenarios
body: <p>I have 3 scenarios in the model
  in the rules() method and I want to use a rule on 2 scenarios ,</p>
  
  <pre><code>[['username', 'email', 'password'], 'required', 'on' =&gt; self::SCENARIO_REGISTER]
  </code></pre>
  
  <p>I read the guide , haven't find a way to bind a rule to 2 scenarios at the same time? Is there any way to do that ?</p>