For docs build, limit scikit-learn version

[stes]

It seems like scikit-learn updated to 1.3.0 a few hours ago (https://pypi.org/project/scikit-learn/#history), but their index for doc build is not updated. This causes and issue that we tracked in https://github.com/AdaptiveMotorControlLab/CEBRA-dev/issues/649.

I propose to temporarily pin sklearn below 1.3.0 only for docs build, which wont affect the main package, to fix this issue. Then, once the object files are updated and published by sklearn, we can unpin again. I will set a reminder to do that within a few weeks.

This will otherwise block merging a few PRs in the upcoming days.

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Fix https://github.com/AdaptiveMotorControlLab/CEBRA-dev/issues/649

[github-actions]

Docstring Coverage Report

Name	Total	Miss	Cover	Cover%
main.py	5	1	4	80%
config.py	6	4	2	33%
data/datatypes.py	5	2	3	60%
data/helper.py	6	1	5	83%
data/multi_session.py	12	5	7	58%
datasets/demo.py	8	3	5	62%
datasets/gaussian_mixture.py	3	2	1	33%
datasets/hippocampus.py	7	1	6	86%
datasets/save_dataset.py	4	1	3	75%
datasets/allen/single_session_ca.py	9	3	6	67%
distributions/discrete.py	9	2	7	78%
distributions/multisession.py	5	1	4	80%
integrations/sklearn/helpers.py	2	1	1	50%
integrations/sklearn/metrics.py	3	1	2	67%
integrations/sklearn/utils.py	6	1	5	83%
models/projector.py	12	9	3	25%
------------------------------------------	--------	-------	--------	---------
TOTAL	396	38	358	90.4%
(45 of 61 files omitted due to complete coverage)

RESULT: PASSED (minimum: 90.0%, actual: 90.4%)