Update Zig.gitignore by adding zig-pgk/

As announced in the devlog https://ziglang.org/devlog/2026/#2026-02-06 all dependencies will now be fetched in the `zig-pgk` directory.
Unless you have a specific reason to include them in your source code, they should be ignored.

Author: alberic89

Zig.gitignore

@@ -1,3 +1,4 @@
 .zig-cache/
 zig-out/
+zig-pkg/
 *.o