Prevent "Creation of dynamic property" (Deprecated on PHP 8.2)

[caiojhonny]

Hello Roberto,

With the new changes I forgot to declare the "monthPart" variable and this generates a new alert:

DEPRECATED Creation of dynamic property robertogallea\LaravelCodiceFiscale\CodiceFiscale::$monthPart is deprecated in vendor/robertogallea/laravel-codicefiscale/src/CodiceFiscale.php on line 154.

I corrected and tested, thank you

Types of changes

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• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

[robertogallea]

I remove the field $this->monthPart and used just $monthPart local variable.

Thank you again