Use template-covariant in CompositeRule

[staabm]

Fixes

------ ----------------------------------------------------------------------- 
  Line   tests/Rules/PHPUnit/DataProviderDataRuleTest.php                       
 ------ ----------------------------------------------------------------------- 
  24     Parameter #1 $rules of class PHPStan\Testing\CompositeRule             
         constructor expects array<PHPStan\Rules\Rule<PhpParser\Node>>, array{  
         PHPStan\Rules\PHPUnit\DataProviderDataRule,                            
         PHPStan\Rules\Methods\CallMethodsRule} given.                          
         🪪  argument.type                                                      
         💡  Template type TNodeType on class PHPStan\Rules\Rule is not         
         covariant. Learn more: https://phpstan.org/blog/whats-up-with-templat  
         e-covariant                                                            
 ------ ----------------------------------------------------------------------- 

in phpstan/phpstan-phpunit#238

[ondrejmirtes]

This fixes the problem but it's a hack 😊 I just forced the rules array type with @var.