Update float subrepo

The debian signing key from a/i expired, so we need to update at least that.

What I meant: git subrepo pull (merge) float

subrepo:
  subdir:   "float"
  merged:   "37d896ff"
upstream:
  origin:   "https://git.autistici.org/ai3/float.git"
  branch:   "master"
  commit:   "66a65304"
git-subrepo:
  version:  "0.4.3"
  origin:   "https://github.com/ingydotnet/git-subrepo"
  commit:   "2f68596"