feat(zig): be less strict on the zig executable

[chpf]

Some zig version managers (notably the popular https://github.com/marler8997/anyzig ) hog the zig executable.
Anyzig in particular does not return success on an invocation without a build.zig.zon with the field minimum_zig_version in the cwd.

This change makes the zig executable check less strict on the assumptions of the zig executable and simply checks if it is present and callable.
This change makes cargo build work when zig is installed via anyzig.

Works on my machine™️

[dmtrKovalenko]

that's cool - will it figure out that this project requires 0.16 version of zig ?

[chpf]

Anyzig looks at the build.zig.zon of the folder and downloads/executes whatever version is specified in the minimum_zig_version field. Its works with master-commits, version tags and whatever seamlessly. I've been using it for a while since it essentially removes the need to think about what zig I've installed for which project as long as it uses the zig build system.

I can't see the CI failure btw. Github just shows an empty error box and shat itself. Since this change was tiny I just tested it locally on windows 11, don't know what went wrong.