Fix VAT Syntax Checker for new Belgian VAT numbers

[Karting06]

Since September 2023, new Belgian enterprise numbers (CBE) starts with a 1 instead of 0.
This is also applicable for VAT numbers because the numbers are the same.

The calculation of the check digits is the same as before.

[phax]

thanks a million :)

[phax]

For the record: https://economie.fgov.be/en/themes/enterprises/crossroads-bank-enterprises/registration-crossroads-bank confirms:

Company Registration Number

Upon registration in the CBE each entity receives a company registration number. The use of this number is required by law. The company registration number is a unique identification number consisting of 10 digits, starting with 0 or 1.

The company registration number assigned to a natural person is not transferable to another entity, even if that entity is a company incorporated by that natural person alone. It shall remain attributed to the same natural person, even if that person interrupts or suspends the activity giving rise to registration and even if the nature of the activity he or she carries out changes.

The company registration number assigned to a legal person is also not transferable to another entity.