Use GitHub Actions for Surge push

[wd15]

Switch the Surge push to use GitHub Actions.

Fixes #1429

The push occurs with an event that does not use a pull_request trigger, but a workflow_run trigger. This needed to be tested from master, not a pull request, see the new surge.yml file on master. The pullrequest.yml file on this branch triggers the surge.yml workflow.

• The comment back to the PR can be seen below.
• I don't know how to update the Surge token (the current one is exposed), see https://github.com/sintaxi/surge/issues/491
• The Nix Cache has been fixed and actually works now
• The Surge teardown will be implemented in a separate PR.

Remember to tear down the live site when merging or closing this pull request.

[pfhub]

The new version of the PFHub website is available at https://random-cat-1467.surge.sh

[pfhub]

@, the new version of the PFHub website is available at https://random-cat-1467.surge.sh

[pfhub]

@, the new version of the PFHub website is available at https://random-cat-1467.surge.sh

[pfhub]

@, the new version of the PFHub website is available at https://random-cat-1467.surge.sh

[pfhub]

@wd15, the new version of the PFHub website is available at https://random-cat-1467.surge.sh

[pfhub]

@wd15, the new version of the PFHub website is available at https://random-cat-1467.surge.sh

[pfhub]

@wd15, the new version of the PFHub website is available at https://random-cat-1467.surge.sh

[pfhub]

@wd15, the new version of the PFHub website is available at https://random-cat-1467.surge.sh

[pfhub]

@wd15, the new version of the PFHub website is available at https://random-cat-1467.surge.sh