Fix too opinionated validation of ISBN-13 code starting with 979

Author: dekoza

barcode/isxn.py

@@ -53,8 +53,6 @@ def __init__(
         self.isbn13 = isbn
         if isbn[:3] not in ("978", "979"):
             raise WrongCountryCodeError("ISBN must start with 978 or 979.")
-        if isbn[:3] == "979" and isbn[3:4] not in ("1", "8"):
-            raise BarcodeError("ISBN must start with 97910 or 97911.")
         super().__init__(isbn, writer, no_checksum, guardbar, addon)