package/gnupg2: security bump to version 2.2.23

package/gnupg2: security bump to version 2.2.23

Fixes the following security issues:

CVE-2020-25125: Importing an OpenPGP key having a preference list for AEAD
algorithms will lead to an array overflow and thus often to a crash or other
undefined behaviour (affected: 2.2.21 / 2.2.22)

For more details, see the announcement:
https://lists.gnupg.org/pipermail/gnupg-announce/2020q3/000448.html

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>