Publish code coverage

[JoerivanEngelen]

On Gitlab, we used to publish our code coverage. This unfortunately broke sometime before the migration to Github, and it was therefore also not migrated. Would be useful to have this again, as we might be able to use this to verify if a PR doesn't result in a decreased code coverage.

We should be careful that no integration tests are accounted for in the coverage tests.

[Huite]

The coverage of the integration test is worth something in making sure there's no syntax errors and the like.

But I guess that's taken care of by the linting now.