GitHub Docker image needs fixing before it can be used as a Github repository

[gaurav]

One nice feature of the GitHub Docker image generated by PR #106 is that it includes the .git directory, so that it can be used as a Git repository. This is hugely helpful in development, since I can switch to a new branch and try that code out very easily when Babel is run on a Kubernetes node.

However, there is one flaw with this .git directory: one of our GitHub action steps (probably docker/login-action@v1) uses Basic authentication to authenticate with GitHub. This instruction remains in the .git/config file, and needs to be manually deleted before git fetch will work.

There must be a way of configuring this action so it doesn't do this, or of removing this section before creating the Docker image, but since it's relatively easy to fix by hand, I'm going to file this away for later.

[gaurav]

It looks like this can be fixed by setting persist-credentials: false in the settings as per https://github.com/marketplace/actions/checkout