Bump workflows to Ubuntu 26.04

[IsaacG]

No description provided.

[BNAndras]

I’m not too worried about the vint CI failing at the moment. I’ll take a look at fixing it in about a week if someone doesn’t beat me to it.

[IsaacG]

I’m not too worried about the vint CI failing at the moment. I’ll take a look at fixing it in about a week if someone doesn’t beat me to it.

It's using a pinned Python setup action that's trying to pull in Python 3.9 which is too old. I'll bump the version of that.

[IsaacG]

vim-vint looks like it hasn't been touched in 3 years. It breaks on 3.12 with some of the package tooling changes. See Vimjas/vint#394
Using 3.11 for now which should be good until 2027-10.