[BUGFIX] Use nullable types for currentPage and lastPage parameters in FormHooks

[konradmichalik]

This PR fixes the following PHP 8.4 deprecations in the FormHook class:

PHP Deprecated:  TRITUM\RepeatableFormElements\Hooks\FormHooks::afterInitializeCurrentPage(): Implicitly marking parameter $currentPage as nullable is deprecated, the explicit nullable type must be used instead in /var/www/html/vendor/tritum/repeatable-form-elements/Classes/Hooks/FormHooks.php on line 36

Deprecated: TRITUM\RepeatableFormElements\Hooks\FormHooks::afterInitializeCurrentPage(): Implicitly marking parameter $currentPage as nullable is deprecated, the explicit nullable type must be used instead in /var/www/html/vendor/tritum/repeatable-form-elements/Classes/Hooks/FormHooks.php on line 36
PHP Deprecated:  TRITUM\RepeatableFormElements\Hooks\FormHooks::afterInitializeCurrentPage(): Implicitly marking parameter $lastPage as nullable is deprecated, the explicit nullable type must be used instead in /var/www/html/vendor/tritum/repeatable-form-elements/Classes/Hooks/FormHooks.php on line 36

Deprecated: TRITUM\RepeatableFormElements\Hooks\FormHooks::afterInitializeCurrentPage(): Implicitly marking parameter $lastPage as nullable is deprecated, the explicit nullable type must be used instead in /var/www/html/vendor/tritum/repeatable-form-elements/Classes/Hooks/FormHooks.php on line 36
PHP Deprecated:  TRITUM\RepeatableFormElements\Hooks\FormHooks::userWentBackToPreviousStep(): Implicitly marking parameter $currentPage as nullable is deprecated, the explicit nullable type must be used instead in /var/www/html/vendor/tritum/repeatable-form-elements/Classes/Hooks/FormHooks.php on line 152

Deprecated: TRITUM\RepeatableFormElements\Hooks\FormHooks::userWentBackToPreviousStep(): Implicitly marking parameter $currentPage as nullable is deprecated, the explicit nullable type must be used instead in /var/www/html/vendor/tritum/repeatable-form-elements/Classes/Hooks/FormHooks.php on line 152
PHP Deprecated:  TRITUM\RepeatableFormElements\Hooks\FormHooks::userWentBackToPreviousStep(): Implicitly marking parameter $lastPage as nullable is deprecated, the explicit nullable type must be used instead in /var/www/html/vendor/tritum/repeatable-form-elements/Classes/Hooks/FormHooks.php on line 152

Deprecated: TRITUM\RepeatableFormElements\Hooks\FormHooks::userWentBackToPreviousStep(): Implicitly marking parameter $lastPage as nullable is deprecated, the explicit nullable type must be used instead in /var/www/html/vendor/tritum/repeatable-form-elements/Classes/Hooks/FormHooks.php on line 152

[akiessling]

Would be great to get this in a new release!