docs: fix phpdocs for PHPStan analyze

[datamweb]

------ ----------------------------------------------------------------------- 
  Line   tests/Language/ItalianTranslationTest.php                              
 ------ ----------------------------------------------------------------------- 
  12     Property                                                               
         Tests\Language\ItalianTranslationTest::$excludedLocaleKeyTranslations  
         (array<string, string>) does not accept default value of type          
         array<int, string>.                                                    
 ------ ----------------------------------------------------------------------- 

https://github.com/codeigniter4/shield/actions/runs/3497594223/jobs/5856927086

[datamweb]

Implemented example:

https://github.com/codeigniter4/translations/blob/e5605931bd0f53f5199d9237a690e3fc6e5b2029/tests/Language/BosnianTranslationTest.php#L19-L22

PHPDocs :
https://github.com/codeigniter4/translations/blob/e5605931bd0f53f5199d9237a690e3fc6e5b2029/tests/Language/AbstractTranslationTestCase.php#L83