stand: bump arbitrary build date to 2024-01-01

For build reproducibility we set PE headers to an arbitrary timestamp.
Nothing in FreeBSD uses this timestamp, but bump it from 2016 to 2024 so
that the timestamp does not seem "too old" in case some third party tool
is used to inspect EFI boot components.

Reviewed by: imp
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D46527