gnupg2: update to 2.5.19

gnupg2: update to 2.5.19

Update GnuPG to the current upstream stable release. As listed at
https://gnupg.org/download/, the 2.5.x series is currently 'stable'
while 2.4.x is 'oldstable' (LTS).

Highlights of changes since 2.4.8:
 * New OpenPGP key formats: Curve25519 and Curve448 (RFC9580)
 * SHA3 family signature support
 * Kyber post-quantum hybrid keys
 * KEM (Key Encapsulation Mechanism) operations
 * dirmngr: improved LDAP and HTTP keyserver support
 * scdaemon: better support for new smartcard tokens
 * Many bug fixes and security improvements

Link: https://dev.gnupg.org/source/gnupg/browse/master/NEWS
Link: https://gnupg.org/download/release_notes.html
Signed-off-by: Daniel Golle <redacted>