docs: fix PHPDoc types in BaseModel

[kenjis]

Description

• fix PHPDoc types

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  Line   src/Models/LoginModel.php                                                
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  37     Property CodeIgniter\Shield\Models\LoginModel::$validationRules          
         (list<string>|string) does not accept default value of type              
         array{ip_address: 'required', id_type: 'required', identifier:           
         'permit_empty|string', user_agent: 'permit_empty|string', user_id:       
         'permit_empty', date: 'required'}.                                       
         💡 Type #1 from the union: array{ip_address: 'required', id_type:         
            'required', identifier: 'permit_empty|string', user_agent:            
            'permit_empty|string', user_id: 'permit_empty', date: 'required'} is  
            not a list.                                                           
 ------ ------------------------------------------------------------------------- 

https://github.com/codeigniter4/shield/actions/runs/8480994004/job/23237640319

Checklist:

• Securely signed commits
• [] Component(s) with PHPDoc blocks, only if necessary or adds value
• [] Unit testing, with >80% coverage
• [] User guide updated
• Conforms to style guide