[ci] R artifact build job is broken

[jameslamb]

See https://github.com/microsoft/LightGBM/runs/1404264739?check_suite_focus=true

The job defined in https://github.com/microsoft/LightGBM/blob/master/.github/workflows/r_artifacts.yml is currently breaking, with this error

To create a local Git repository instead, add Git 2.18 or higher to the PATH
Error: Input 'submodules' not supported when falling back to download using the GitHub REST API. To create a local Git repository instead, add Git 2.18 or higher to the PATH.

[jameslamb]

I've marked this "good first issue" because it isn't urgent and I'm guessing that template is just missing an apt-get insall git somewhere. If you'd like to work on this, please add a comment here.

[github-actions]

This issue has been automatically locked since there has not been any recent activity since it was closed. To start a new related discussion, open a new issue at https://github.com/microsoft/LightGBM/issues including a reference to this.