Support non-ephemeral runners

[toast-gear]

Feature
Ensure that any files / folders that get touched by this action in the mounted workspace have thier permissions fixed back to their original owner (probably the owner of the $GITHUB_WORKSPACE)

Problem
As it stands when you use this action the .terraform folder will have its owner set to root root as the container makes changes to the files (as well as any other file or folder the container creates / updates). This then results in the next run of the workflow failing as the checkout action fails to delete the .terraform folder due to it being owned by root root rather than the user running the actions service.

To wokraround this you can use the action peter-murray/reset-workspace-ownership-action to reset the permissions on the repository code.

      - name: Get Actions user id
        id: get_uid
        run: |
          actions_user_id=`id -u $USER`
          echo $actions_user_id
          echo ::set-output name=uid::$actions_user_id
      - name: Correct Ownership in GITHUB_WORKSPACE directory
        uses: peter-murray/reset-workspace-ownership-action@v1
        with:
          user_id: ${{ steps.get_uid.outputs.uid }}

This is faff though and needs to be done in any workflow that uses this action, it should be handled natively or there be an input that can solve this.

https://vsupalov.com/docker-shared-permissions/ Basically support this problem.

EDIT For posterity's sake this is the type of error you'll get due to docker messing with the permission bits of files / folders it touches:

Run actions/checkout@v2
Syncing repository: owner/repo
Getting Git version info
Deleting the contents of '/actions-runner/_work/repo/repo'
Error: Command failed: rm -rf "/actions-runner/_work/repo/repo/.terraform"
rm: cannot remove '/actions-runner/_work/repo/repo/.terraform/modules/modules.json': Permission denied