Conferences: add Go Conference 2026

Co-authored-by: Takuma Shibuya <shibuuuu5@gmail.com>
Co-authored-by: Ryoko Tominaga <ryokotmng@gmail.com>
Co-authored-by: Kengo Sato <kengo.carp.no1@gmail.com>

Change-Id: I73e78a85b2a58c2027e87cab712afc071206bab5
Reviewed-on: https://go-review.googlesource.com/c/wiki/+/798120
Auto-Submit: Jorropo <jorropo.pgm@gmail.com>
Reviewed-by: Jorropo <jorropo.pgm@gmail.com>
Commit-Queue: Jorropo <jorropo.pgm@gmail.com>