Support selecting the installed runtime architecture

The actions/setup-node action supports an architecture input for selecting the target architecture of the installed Node.js runtime.

It would be super useful if pnpm/setup provided the same capability for runtimes installed through pnpm runtime set.

My use case is testing an x86_64-apple-darwin native addon on macOS. I would like to use a macos-latest runner while installing x64 Node.js and running it through Rosetta, rather than depending on GitHub's Intel macOS runners.

For example:

- uses: pnpm/setup@v2
  with:
    runtime: node@24
    architecture: x64

When omitted, architecture should continue to default to the runner's architecture.
The expected result on an ARM64 macOS runner would be an x64 Node.js runtime:

- run: test "$(node -p process.arch)" = "x64"

I realize pnpm runtime set may also need support for selecting a target architecture before the action can pass this through. If so, guidance on whether this request belongs in pnpm/pnpm instead would be appreciated.

Start by reading the pnpm/setup action's handling of the runtime input and the related pnpm runtime set behavior in pnpm/pnpm. Check how architecture is represented for Node.js on ARM64 macOS, then verify the example with node -p process.arch; done means an omitted architecture preserves the runner default and x64 selects an x64 runtime.