There's a closed pull request on the void-packages repository

gnunet: update to 0.19.3
https://github.com/void-linux/void-packages/pull/43019

Description:
0.12.2 is not even available on the ftp server anymore, so I took the liberty to update it.

#### Testing the changes
- I tested the changes in this PR: **briefly** (I don't know much about GNUnet, but it builds and from a high-level look it runs, but I failed to test GNS functionality)

#### Local build testing
- I built this PR locally for my native architecture, x86_64-glibc