`test_discretizer.py` raises warnings

[zzril]

Describe the bug

test_discretizer.py produces 6 warnings that are currently not catched by the tests.

To Reproduce

Checkout main.
(For reference: I observed the behaviour on commit 5e3da8d.)

Run pytest from the console. (Or poetry run pytest.)

9 warnings will be shown.
(Note that the first 3 are already addressed by current PR #425.)

Expected behavior

Test should not raise warnings.

If the warnings are supposed to be raised, catch them in the tests.
If they are not raised by us, understand why they happen and change the library code in a way that does not generate warnings. (If nothing else works, silence them in our library code.)