[build.zig.zon] Fix: replace deleted hexops/xcode-frameworks with pkg…

[LewisLee26]

The xcode-frameworks GitHub repo no longer exists, causing zig fetch to fail on macOS builds. This replaces the URL with the machengine mirror.

The URL was taken from the mach build.zig.zon which uses the updated mirror.

Run zig build --release=fast -Dtarget=aarch64-macos -Dsysroot "$SDKROOT"
  zig build --release=fast -Dtarget=aarch64-macos -Dsysroot "$SDKROOT"
  shell: /bin/bash -e {0}
  env:
    ZIG_GLOBAL_CACHE_DIR: /Users/runner/work/xcode_test/xcode_test/.zig-cache
    ZIG_LOCAL_CACHE_DIR: /Users/runner/work/xcode_test/xcode_test/.zig-cache
    SSL_CERT_FILE: /Users/runner/work/xcode_test/xcode_test/cert.pem
    SDKROOT: /Applications/Xcode_16.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX15.5.sdk
.zig-cache/p/raylib-5.6.0-dev-whq8uKcqDQWBSifz7ukF2u4sZUlgZxcrN5_p3ONMw1Sy/build.zig.zon:10:20: error: unable to discover remote git server capabilities: ProtocolError
            .url = "git+https://github.com/hexops/xcode-frameworks#9a45f3ac977fd25dff77e58c6de1870b6808c4a7",
                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[raysan5]

@LewisLee26 thanks for the review