Fixed PHPStan rule error identifiers

[mikadamczyk]

🎫 Issue	N/A

Description:

Fixes:

 ------ -------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 
  Line   rules/RequireClosureReturnTypeRule.php                                                                                                                                    
 ------ -------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 
  35     Method Ibexa\PHPStan\Rules\RequireClosureReturnTypeRule::processNode() should return list<PHPStan\Rules\IdentifierRuleError> but returns array{PHPStan\Rules\RuleError}.  
         🪪  return.type                                                                                                                                                           
         💡  Error is missing an identifier. See: https://phpstan.org/blog/using-rule-error-builder                                                                                
         at rules/RequireClosureReturnTypeRule.php:35  

For QA:

Documentation: