maint(common): Integrate pre-release of langtags.json

[darcywong00]

WS tech is planning to do a production release of langtags.json (tentatively Jan 30, 2026)
Repo
https://github.com/silnrsi/langtags

Staging:
https://ldml.api.sil.org/langtags.json?staging=1

We should do a smoke test of having test build run the tests