pgpkeys: use full keyid to trust Linus' key

It's possible for fingerprints to collide.
To avoid that people accidentally trust an impersonated key document the
full key fingerprint.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/r/20230716-keyid-v1-1-bf14426a8279@weissschuh.net
Signed-off-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>