ci: publish test reports for mypy and pytest

[aucampia]

Summary of changes

Use the dorny/test-reporter GitHub Action to publish test reports for
both mypy and pytest.

This should make it easier to see what fails without having to dig
through the rather noisy console logs.

Checklist

• Checked that there aren't other open pull requests for
  the same change.
• Checked that all tests and type checking passes.
• Considered granting push permissions to the PR branch,
  so maintainers can fix minor issues and keep your PR up to date.

[aucampia]

The reports will only start working once this is merged to master but for an example see: \

• PR: ci: publish test reports aucampia/rdflib#40
• Test failure: https://github.com/aucampia/rdflib/runs/7932777048?check_suite_focus=true
• Test pass: https://github.com/aucampia/rdflib/pull/40/checks?check_run_id=7932854039

One caveat is that xfails get reported as skips, but otherwise the output is useful for seeing what specific tests failed and even seeing the output on failure.

[coveralls]

Coverage remained the same at 90.461% when pulling bbe64f5 on aucampia:iwana-20220820T1323-test_report into a39d143 on RDFLib:master.

[ghost]

nice touch