Some warnings are not captured by pytest

[m-mohr]

Some warnings are not correctly captured by pytest after the changes in #27.

Instead of showing up in the warnings summary:

They now show up in the live log setup:

That is confusing. They are also not identified as warnings by pytest. Is there a way to fix this, @soxofaan ?

Originally posted by @m-mohr in #32 (comment)

Code to run this: pytest src/openeo_test_suite/tests/processes/processing/test_example.py --runner=dask --log-cli-level=WARN --processes divide,array_append > output.txt

[soxofaan]

I'm just going to revert this warning to warnings.warn if that makes more sense to you.
This is warning is basically a todo that has to be addressed anyway, it's not worth it to overthink if this has to be logging.warning vs warnings.warn

[soxofaan]

one minor thing: I changed the warning message from ...but got {result.__class__} to ...but got {result!r} because the latter gives more information and context (exception class + message) instead of just exception class