fix: use correct arch on macOs for cache key

[Lucino772]

Description

I am getting the following error when running this action on an Intel macOS runner:

Received 26451860 of 26451860 (100.0%), 19.3 MBs/sec
Cache Size: ~25 MB (26451860 B)
/usr/local/bin/gtar -xf /Users/runner/work/_temp/c8303197-5442-4088-a86a-22e1197bea7b/cache.tzst -P -C /Users/runner/work/REPOSITORY_NAME/REPOSITORY_NAME --delay-directory-restore --use-compress-program unzstd
Cache restored successfully
Found Tailscale 1.90.6 in cache: /Users/runner/hostedtoolcache/tailscale/1.90.6/macOS-amd64
▶️ copy tailscale from cache
▶️ copy tailscaled from cache
▶️ chmod tailscale
▶️ chmod tailscaled
Starting tailscaled daemon...
node:internal/child_process:421
Waiting for tailscaled daemon to become ready...
    throw new ErrnoException(err, 'spawn');
▶️ get tailscale status
          ^

Error: spawn Unknown system error -86
    at ChildProcess.spawn (node:internal/child_process:421:11)
    at Object.spawn (node:child_process:796:9)
    at ToolRunner.<anonymous> (/Users/runner/work/_actions/tailscale/github-action/v4/dist/index.js:4822:34)
    at Generator.next (<anonymous>)
    at /Users/runner/work/_actions/tailscale/github-action/v4/dist/index.js:4436:71
    at new Promise (<anonymous>)
    at __webpack_modules__.6665.__awaiter (/Users/runner/work/_actions/tailscale/github-action/v4/dist/index.js:4432:12)
    at /Users/runner/work/_actions/tailscale/github-action/v4/dist/index.js:4804:53
    at new Promise (<anonymous>)
    at ToolRunner.<anonymous> (/Users/runner/work/_actions/tailscale/github-action/v4/dist/index.js:4804:20) {
  errno: -86,
  code: 'Unknown system error -86',
  syscall: 'spawn'
}

Node.js v24.10.0

After doing some research, I discovered that both ARM and Intel macOS runners are using the same cache key:
tailscale/1.90.6/macOS-amd64.

Because of this, the first run on an ARM runner built and cached an ARM-compiled Tailscale binary. On a subsequent run, an Intel runner restored that cached binary, but since the binary was built for a different architecture, it failed to run.

macos-13 (Intel):

Found Tailscale 1.90.6 in cache: /Users/runner/hostedtoolcache/tailscale/1.90.6/macOS-amd64

macos-15 (ARM64):

Found Tailscale 1.90.6 in cache: /Users/runner/hostedtoolcache/tailscale/1.90.6/macOS-amd64

Solution

This PR fixes the getTailscaleArch function so that ARM macOS runners return the correct architecture, ensuring that the generated cache key uses the correct architecture. On macOS runners specifically, config.arch is only ever used when generating the cache key, it isn’t passed to the Go build command at all.

PS: As a temporary fix, disabling the cache on macOS runners allows the workflow to run successfully

[mpminardi]

Thank you for this @Lucino772 , and apologies for the miss here!