Update Go to 1.26 before the branch

[Benny Siegert <bsiegert%netbsd.org@localhost>]

Hi!

Before the Q2 branch, I would like to change the default Go version to 
1.26. Typically, there is a small number of failing packages due to this 
(five or less). I run a bulk build to find these.

However, this time around, due to travelling, I might not be able to run 
the bulk build before ~ March 3. Would it still be okay to do the version 
bump? I promise I will fix the breakage before we release :)

--
Benny