Fix ISOCodes magic methods phpdocs

[jeanlucnguyen]

If you don't put the parenthesis, they are not recognized as valid by phpstan.

  :14    PHPDoc tag @method has invalid value (\Juanparati\ISOCodes\Models\ContinentModel  
         continents): Unexpected token "\n * ", expected '(' at offset 109                 
  :14    PHPDoc tag @method has invalid value (\Juanparati\ISOCodes\Models\CountryModel    
         countries): Unexpected token "\n * ", expected '(' at offset 171                  
  :14    PHPDoc tag @method has invalid value (\Juanparati\ISOCodes\Models\CurrencyModel   
         currencies): Unexpected token "\n * ", expected '(' at offset 235                 
  :14    PHPDoc tag @method has invalid value                                              
         (\Juanparati\ISOCodes\Models\CurrencyNumberModel currencyNumbers): Unexpected     
         token "\n * ", expected '(' at offset 310                                         
  :14    PHPDoc tag @method has invalid value (\Juanparati\ISOCodes\Models\LanguageModel   
         languages): Unexpected token "\n ", expected '(' at offset 373

[jeanlucnguyen]

https://phpstan.org/writing-php-code/phpdocs-basics#magic-methods