♻️ Refactor tests to be more readable (follow-up to #807)

[s-weigand]

Is your feature request related to a problem? Please describe.

Currently, most of the tests use Model.from_dict with 20+ lines dicts to define the model and this makes it harder to spot the differences between tests and to detect problems in tests.
#807 implements a simple draft of how tests could be refactored and made more readable.

Describe the solution you'd like

While tests should be verbose, they should also be readable and understandable.
Thus an autogenerated model dict generated by only the needed parameters as proposed in #807 would help to simplify tests and make it a lot easier to spot the differences between tests and detect errors.

Since this would be a test refactor it should only change:

1. Tests which use Model.from_dict
2. The model dict generators in glotaran.testing

Additional context

The tests that could quickly be changed are listed in #807 (comment)

[s-weigand]

Taken by @fidelak

[jsnel]

After some further consideration we realize that we currently don't have "good first issues" that don't require some amount of domain knowledge, so I removed that label. See also: #837

If you did manage to do something already @fidelak please let us know, but if you didn't start yet then no worries, we'll pick this up internally.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been closed due to lack of recent activity. Please open a new issue if you're still encountering this problem. Thanks for your contributions!