Current test suite doesn't cover the subsecond formatting at all and toml11 is quite finicky with that. We should at the very least test its behavior to avoid silent breakages on updates. (cherry picked from commit 7ed0229d1abd4414144c7af396842462ce6fc1eb) Upstream-PR: https://github.com/NixOS/nix/pull/13741 Change-Id: I6a6a696433b168072d6ad2585dce8a3c10ccbc39