Remove grid_search_models/ after running tests

[stes]

Our Makefile contains a routine for removing temp files created during testing via make clean_test. One of the added folders for testing the grid search function was not included there, this PR fixes that.

[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%)

[MMathisLab]

LGTM, but some tests are failing

[stes]

Thanks -- failing tests still due to https://github.com/AdaptiveMotorControlLab/CEBRA-dev/pull/647, working on that with @gonlairo