[ci] temporarily pin scipy version and fix Python linting error

[StrikerRUS]

Unblock CI in this repo.

Temp workaround for #5390.

[jameslamb]

Thanks for this! I can work on trying to remove these pins in the future.

---

I checked, and I'm guessing the new linting error (build link) is caused by the release of pycodestyle 2.9.0 about 3 days ago: https://pypi.org/project/pycodestyle/#history. Maybe it just made it to conda-forge.

Linting Python code
./python-package/lightgbm/basic.py:1510:31: E275 missing whitespace after keyword

I don't need to re-approve when you fix that...I'm in favor of altering the code in basic.py to comply with what pycodestyle wants, but I trust whatever decision you make about that.

[StrikerRUS]

At first, I thought that that linting CI job fail is a false positive, but after a precise check I see we really have a linting error in our codebase. No whitespace after not operator:

LightGBM/python-package/lightgbm/basic.py

Line 1510 in cdc83a5

if not(isinstance(params[cat_alias], list) and set(params[cat_alias]) == categorical_indices):

https://stackoverflow.com/a/59395093

[jameslamb]

No whitespace after not operator:

Wow! I stared at that line for a long time and also wasn't sure what it was complaining about. Great work.

[github-actions]

This pull request has been automatically locked since there has not been any recent activity since it was closed. To start a new related discussion, open a new issue at https://github.com/microsoft/LightGBM/issues including a reference to this.