Updated BE format documentation

The first number of a Belgian VAT number can also be a 1. Numbers starting with a 1 are estimated to be issued as of september 2023.

See https://economie.fgov.be/en/themes/enterprises/crossroads-bank-enterprises/actualities/structure-company-number-first.

src/Vies/Validator/ValidatorBE.php

@@ -18,7 +18,7 @@
  * VAT format: [C0 C1 C2 C3 C4 C5 C6 C7 C8 C9]
  *
  * Range:
- *      C0 Always the digit '0'
+ *      C0 Either 0 or 1 (starting september 2023)
  *      C1 Numeric from 1 to 9
  *      C2 ... C9 Numeric from 0 to 9
  *