Check that removing codecov token works on a new org

Codecov [now supports tokenless uploads](https://docs.codecov.com/docs/codecov-tokens#uploading-without-a-token).

However this did not work for a fresh repo in a fresh org: https://github.com/codecov/codecov-action/issues/1891

The issue was on their end, so this may have been a one off.

This ticket is to repeat the experiment:
- Create a new GitHub org
- Create a new copier template project within it following all the docs apart from the codecov one
- Remove the secret from `.github/workflows/_test.yml`
- Push the results
- Check the CI logs for the codecov action to see that it uploads correctly

If this works then update the instructions in this repo and remove the codecov secret from `ci.yml` and `_test.yml` file