Support `GB` talker id for BaiDou

[RubixDev]

From what I've gathered online, it seems like the BD identifier was used in the past, but the newer standard is GB. I would suggest simply accepting both.

nmea0183/src/lib.rs

Line 180 in a6ad7a8

"BD" => Ok(Source::Beidou),

Well at least my NEO-M9N chip seems to send the messages with GB.