Clean up testing with optimagic after releases

[timmens]

Testing with optimagic is currently only possible locally with a local tranquilo and local optimagic version. After tranquilo 0.1.0 and optimagic 0.5.3 has been published, adjust the tests such that tranquilo's test suite contains optimagic.

1. Use optimagic consistently in the development and testing env of tranquilo
2. Check whether we can close Make sure that deprecation warnings are handled #15