ci: allow custom actions runner to be defined

[DavideIadeluca]

Fixes #0000

Changes proposed in this pull request: Allow custom GitHub Actions runner to be defined in the reusable frontend & backend workflows. This allows third-party vendors to optionally pass a new input runner_type which specifies on which machine the jobs are being run (be it a custom GitHub-hosted runner or a self-hosted one).

Hypothetical example of a calling workflow:

name: ACME Foobar PHP

on: [workflow_dispatch, push, pull_request]

jobs:
  run:
    uses: flarum/framework/.github/workflows/REUSABLE_backend.yml@2.x
    with:
      enable_backend_testing: true
      enable_phpstan: true
      php_versions: '["8.0", "8.1", "8.2", "8.3"]'
      runner_type: self-hosted

      backend_directory: . 

It's important to note that this new input is optional and will default to ubuntu-latest if not defined by the calling workflow.

Reviewers should focus on:

Screenshot

QA

Necessity

• [ ] Has the problem that is being solved here been clearly explained?
• [ ] If applicable, have various options for solving this problem been considered?
• [ ] For core PRs, does this need to be in core, or could it be in an extension?
• [ ] Are we willing to maintain this for years / potentially forever?

Confirmed

• [ ] Frontend changes: tested on a local Flarum installation.
• [ ] Backend changes: tests are green (run composer test).
• [ ] Core developer confirmed locally this works as intended.
• [ ] Tests have been added, or are not appropriate here.

Required changes:

• [ ] Related documentation PR: (Remove if irrelevant)
• [ ] Related core extension PRs: (Remove if irrelevant)

[DavideIadeluca]

If you are okay with this change, I'm happy to open the same PR against 1.x.

[SychO9]

Thanks for the PR! could you please remove the dist files from the PR, maybe if you branch off the commit in question from your main(2.x) branch to prevent github actions from generating dist files.

Feel free to PR to 1.x as well.

[DavideIadeluca]

Superseded by #3988