Run part of workflow on different stack

Description of the feature request

I would like to be able to set a selected workflow to be run on different stack (e.g. Ubuntu) while the whole build would be run on the primary stack (e.g. macOS).

This would like similar to following:

workflow: build_app (macOS)

  1. _prepare (macOS)
  2. _build iOS app (macOS)
  3. _build Android app (Ubuntu, copy artifacts to macOS)
  4. _deploy app (macOS)

or other:

workflow: ui_tests (macOS)

  1. _prepare (macOS)
  2. _ui_test_ios (macOS)
  3. _ui_test_android (Ubuntu)
  4. _deploy_artifacts (macOS)

Use case / for what or how I would use it

To perform UI tests at the same time for iOS and Android (in Flutter).