Changed bootable interface to inherit so mock can work on PHPUnit 9.

src/Provider/Bootable_Provider_Interface.php

@@ -3,12 +3,13 @@ declare( strict_types=1 );
 
 namespace Rarst\Laps\Provider;
 
+use Pimple\ServiceProviderInterface;
 use Rarst\Laps\Plugin;
 
 /**
  * Interface for providers that need to boot up once plugin is ready to start.
  */
-interface Bootable_Provider_Interface {
+interface Bootable_Provider_Interface extends ServiceProviderInterface {
 
 	/**
 	 * @param Plugin $laps Container instance.