Deprecated warning on php 8.2

[antonlukin]

I get deprecated warning while using Leyka on clear WordPress with php 8.2:

Creation of dynamic property Leyka_Unisender_Extension::$_unisender_system_fields is deprecated
/plugins/leyka/extensions/unisender/leyka-class-unisender-extension.php:37

[Ahaenor]

Thanks! Fixed.