chore: pin zig 0.14 in build.zig.zon (#8871)

Hi!

I'm a full Zig noob but [Mitchell's recent
post](https://mitchellh.com/writing/libghostty-is-coming) made me want
to clone the repo and take a look at the tooling.

My first attempt at running examples though VSCode failed because the
latest version of Zig is 0.15.1, but Ghostty requires Zig 0.14*. When
configuring the extension to use a compatible version if Zig, it
suggested pinning the version in a .zigversion file. I'm not familiar
with the pattern, but if it can help someone else's onboarding, I
figured I'd open a PR to suggest the change.

Cheers

*edit: I had a hard time figuring that out

build.zig.zon

@@ -3,6 +3,7 @@
     .version = "1.2.1",
     .paths = .{""},
     .fingerprint = 0x64407a2a0b4147e5,
+    .minimum_zig_version = "0.14.1",
     .dependencies = .{
         // Zig libs