lang/go123: Update to 1.23.12
While here: golang.org now points to go.dev (thanks to Meng Zhuo in the
Review below).
Changes:
go1.23.12 (released 2025-08-06) includes security fixes to the database/sql and os/exec packages, as well as bug fixes to the runtime. See the Go 1.23.12 milestone (follows) on our issue tracker for details. https://github.com/golang/go/issues?q=milestone%3AGo1.23.12+label%3ACherryPickApproved
Differential Revision: https://reviews.freebsd.org/D50595