ATLASRECTS-6461, ATLINFR-4167: Update lwtnn to version 2.12.1

This updates lwtnn to fix some FTEs reported in ATLASRECTS-6461. You can get the tarball by running

wget https://github.com/lwtnn/lwtnn/archive/refs/tags/v2.12.1.tar.gz

I've update the MD5 sum and path in this MR, I just need someone to move the file.