Support non runner user on self-hosted runners

[fkorotkov]

Ensure the following before filing this issue

• I verified it reproduces with the latest version with - uses: ruby/setup-ruby@v1 (see Versioning policy)

• I tried to reproduce the issue locally by following the workflow steps (including all commands done by ruby/setup-ruby, except for Downloading Ruby & Extracting Ruby),
  and it did not reproduce locally (if it does reproduce locally, it's not a ruby/setup-ruby issue)

Are you running on a GitHub-hosted runner or a self-hosted runner?

self-hosted runner

Link to the failed workflow job (must be a public workflow job, so the necessary information is available)

https://github.com/cirruslabs/actions-playground/actions/runs/8781520697/job/24093712039

Any other notes?

Self-mosted macOS runners not always use runner as the user name. Right now runner user name is hard coded:

setup-ruby/common.js

Lines 267 to 269 in 6bd3d99

	} else if (platform.startsWith('macos-')) {
	return '/Users/runner/hostedtoolcache'
	} else if (platform.startsWith('windows-')) {

Can probably be fixed similar to actions/setup-python#708

[fkorotkov]

Current workaround if you have "admin" user is to run the following first to pre-create /Users/runner:

- name: Ruby Workaround
  run: sudo mkdir -p /Users/runner && sudo chown -R admin:admin /Users/runner

[eregon]

See #584 (comment), it's not fixable.

[eregon]

Basically the same as actions/setup-python#708 (comment) actually