Fix failing tests

[dopefishh]

Some tests are failing:

• test_clean_time_slots
• test_extract
• test_shift_annotations

[dopefishh]

test_clean_time_slots and test_shift_annotations were introduced by #21
For now I've reverted this and we need to think about how to implement it properly (taking this property into account when shifting etc.).

[xrotwang]

I added pytest.mark.xfail to the failing tests in my latest PR, in order to get the CI action to pass. These might need to be removed again when fixing the tests.

[dopefishh]

The problem is not in test_extract but in remove_annotation

[xrotwang]

Ok, I think we should remove the pytest.mark.xfail in any case. I just slightly abused this mechanism to get passing tests once, to make sure the CI integration works as expected.