github ci: pin zig version to 0.13.0 (for now)

[floooh]

Just a quick fix to make the CI work again.

I already fixed the build.zig files in sokol-zig and dcimgui to work both with the latest 0.14.x changes (e.g. for dcimgui just pull the latest version instead of 1.91.6, and check sokol-zig's build.zig updates.

(let me know if you want me to integrate those changes into sokol-d/build.zig or if you want to do that yourself) :)

[kassane]

I have read some of the questions you asked about refactored build.zig redundancies.
However, is there any problem with keeping the master?
like floooh/sokol-zig@a26bb7c

[floooh]

That commit didn't work, the new version looks like this (the if-block is the old version for 0.13.0, and the much simpler else-block is for the current Zig nightly):

https://github.com/floooh/sokol-zig/blob/9d113214f7750f8ab68b465b2605ce308e995fb4/build.zig#L365-L390

...that would be the 'proper' solution of course (instead of pinning the CI to 0.13.0). E.g. feel free to close this PR if you want to fix build.zig instead.

[floooh]

Ah, let me just fix the build.zig instead one sec ;) New PR incoming.

[floooh]

I'll also fix the dcimgui dependency... because that has another breaking change.

[floooh]

...oh there's multiple places to fix in the sokol-d/build.zig...

[floooh]

Ooof, there's a lot more things to fix for Zig 0.14.x, especially when it needs to run both on 0.13 and 0.14. I'll reopen the PR and leave the build.zig changes to you :)

I think it's better to just pin the CI to 0.13.0 for now.

PS: e.g. one other thing that needs fixing is the addArtifact() helper function, since the .root_module Options member is now a pointer.