Check that removing codecov token works on a new org

[coretl]

Codecov now supports tokenless uploads.

However this did not work for a fresh repo in a fresh org: codecov/codecov-action#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