Fix PHPSTAN issues

Problem/Motivation

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  Line   src/Commands/AdvancedQueueCommands.php                                 
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         Ignored error pattern #^Call to method success\(\) on an unknown       
         class Drush\\Style\\DrushStyle\.$# (class.notFound) in path            
         /builds/project/advancedqueue/web/modules/custom/advancedqueue/src/Co  
         mmands/AdvancedQueueCommands.php was not matched in reported errors.   
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  Line   tests/src/Kernel/DatabaseBackendTest.php                            
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  144    Call to method PHPUnit\Framework\Assert::assertEmpty() with 0 will  
         always evaluate to true.                                            
         🪪  method.alreadyNarrowedType                                      
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 [ERROR] Found 2 errors