Authenticate automated commits as Hypothesis GitHub App

[seanh]

Automated PRs from the update_repos.yml workflow authenticate themselves to GitHub as GitHub Hypothesis App but the author of the individual commits is set to GitHub Actions Cookiecutter Workflow (example PR, example commit).

It would be nicer if the commits themselves were also recognised by GitHub as coming from Hypothesis GitHub App and I think this is possible. We need to set the git email address (git config --global user.email "...") to the form userID + name[bot] + @users.noreply.github.com and apparently we can get the right email and user ID from the response from the https://docs.github.com/en/rest/repos/contents#create-or-update-file-contents endpoint (to a request authenticated as the app).