Cannot run workflow on a forked PR

[robg-test]

On a forked PR i.e. #77

The pipeline does not execute because pull requests from forked branches do not have access to the github.event.pull_request.head.ref variable

This is due to security reasons, need to come up with something that will fix this and ideally not hamper the security of any Github secrets (If we choose to have them)

[robg-test]

Still an issue, looks like Github Actions bot cannot commit to the repo. Possibly using the wrong token.

[cmbuckley]

See #95.