[ci] prevent Python tests from leaving behind files

[vnherdeiro]

Contributes to #6361

Prevents the following files from being left behind when the Python tests are run:

• data_dask.csv
• Tree4.gv
• Tree4.gv.pdf

The graphivz artefacts from tests/python_package_test/test_plotting.py now go to the pytest tmp_path and are deleted after test run.

[jameslamb]

Thanks for working on this!

I haven't tested yet if you've caught all the cases where this happens, but these fixes look like what I'd expect. Please see the suggestions I left, and the changes I made to the title and description.

PR titles become commit messages and therefore changelog entries in this repo, so they should describe the changes in a way that would be clear to someone reading the release notes. To see the conventions we follow here, compare these:

• commit log on master: https://github.com/microsoft/LightGBM/commits/master/
• most recent release notes: https://github.com/microsoft/LightGBM/releases/tag/v4.5.0

[vnherdeiro]

Noted and adressed your comments @jameslamb thanks for the prompt review

[jameslamb]

Please update this branch to the latest master (to pull in recent CI fixes), and fix the issues reported at https://github.com/microsoft/LightGBM/actions/runs/10605651987/job/29394936451?pr=6626.

You can fix those by running the following from the root of the repo:

pip install pre-commit
pre-commit run --all-files

[borchero]

Are there any other such occurrences as in #6627 and here? Maybe we can merge all of these changes into a single PR?

[vnherdeiro]

@borchero According to #6361 these are the last two causes of test "leftover" files. I am okay with merging the two PRs.

[borchero]

LGTM :)

[vnherdeiro]

Have now merged #6627 as the total code diff is small and they share the same purpose. I let the moderators close the other PR.

[jameslamb]

Ok thanks very much! I've merged in latest master to get the changes from #6636, will merge this if CI passes.

We really appreciate the help!

[vnherdeiro]

Thanks for the approvals. I am very pleased with this first minor contribution to a package I have been using with enjoyment and satisfaction! Let's see if I can add more to it in the future.