tmux updated to 3.6a

[Thomas Klausner <wiz%netbsd.org@localhost>]

Hi!

I've just updated tmux in the base system to 3.6a.

Please note that when upgrading, you cannot join tmux 3.5a sessions
with tmux 3.6a, so make sure to exit any old sessions before upgrading
your tmux binary.

Cheers,
 Thomas