editors/emacs: Update to 29.3

Emacs 29.3 is an emergency bugfix release intended to fix several
security vulnerabilities. For details, refer to the Changelog.

Changelog: https://git.savannah.gnu.org/cgit/emacs.git/tree/etc/NEWS?h=emacs-29.3

Reviewed by: jrm
Security: f661184a-eb90-11ee-92fc-1c697a616631
Differential Revision: https://reviews.freebsd.org/D44492

Co-authored-by: Joseph Mingrone <jrm@FreeBSD.org>