contrib/tzdata: import tzdata 2025b
Changes: https://github.com/eggert/tz/blob/2025b/NEWS
Approved by: so
Security: FreeBSD-EN-25:04.tzdata
(cherry picked from commit d2cccdef30376b7de5643caae1ef035f8e6932f0)
(cherry picked from commit 475082194ac811a925bf4a8109ef5e4f4f485dad)