Add additional pubkey for dvzrv

pubkeys/dvzrv.pub:
Add additional pubkey, based on the PGP key
`991F6E3F0765CF6295888586139B09DA5BF0D338`.
For chain of trust towards the previously used signing key
`C7E7849466FE2358343588377258734B41C31549`, refer to the output of
`pacman-key --list-sigs 991F6E3F0765CF6295888586139B09DA5BF0D338`.

pubkeys/dvzrv.pub

 ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIHo656zZGq2lK/AhoACM6v6h8rwCbWG4YVwlFjh9es8X dave@dvzrv
 ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIAGqlGt8LVYWzSoewv4Gf7W07BdRuj+3vApq+9Wdvvti openpgp:0xB551DFD6
+ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIHTjZNraF2KN/whbJKX7GQ/b5YzQYUVsrzhY/XVFhHaK openpgp:0xD6B976F5