Update time zone data files to tzdata release 2025c.

Update time zone data files to tzdata release 2025c.

This is pretty pro-forma for our purposes, as the only change
is a historical correction for pre-1976 DST laws in
Baja California.  (Upstream made this release mostly to update
their leap-second data, which we don't use.)  But with minor
releases coming up, we should be up-to-date.

Backpatch-through: 14