There's no git tag for 1.2.3, hence we need to pin to the corresponding
revision because we build from a git source.
After recent breakage on Hydra[1], the tests were disabled. Although
some build machines don't support AVX, we shouldn't use a DLib without
AVX as the builder's result is also used on modern machines with AVX
support. Before merging changes, maintainers should run the check phase
locally in a `nix-shell`.
[1] https://hydra.nixos.org/build/89533530
6fec5aac83