Fix partial dependence graph method failing on multiclass problems when the label is numeric

[angela97lin]

Closes #2114

[codecov]

Codecov Report

Merging #2372 (e37c756) into main (a096a7c) will increase coverage by 10.4%.
The diff coverage is 100.0%.

@@           Coverage Diff            @@
##            main   #2372      +/-   ##
========================================
+ Coverage   89.3%   99.7%   +10.4%     
========================================
  Files        281     281              
  Lines      24907   24926      +19     
========================================
+ Hits       22222   24829    +2607     
+ Misses      2685      97    -2588     

Impacted Files	Coverage Δ
evalml/model_understanding/graphs.py	100.0% <100.0%> (+44.4%)	⬆️
...del_understanding_tests/test_partial_dependence.py	100.0% <100.0%> (+42.8%)	⬆️
evalml/automl/automl_search.py	99.4% <0.0%> (+0.2%)	⬆️
evalml/tests/utils_tests/test_logger.py	100.0% <0.0%> (+0.6%)	⬆️
evalml/pipelines/utils.py	99.1% <0.0%> (+1.0%)	⬆️
evalml/tests/conftest.py	99.6% <0.0%> (+1.1%)	⬆️
...derstanding/prediction_explanations/_algorithms.py	98.9% <0.0%> (+1.2%)	⬆️
...s/prediction_explanations_tests/test_explainers.py	100.0% <0.0%> (+1.8%)	⬆️
evalml/tests/component_tests/test_estimators.py	100.0% <0.0%> (+1.9%)	⬆️
evalml/tests/component_tests/test_components.py	100.0% <0.0%> (+2.8%)	⬆️
... and 42 more

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[angela97lin]

@freddyaboulton I'm sure you might have some opinions about me adding yet another long running test 😂 I wasn't confident in a way to mock things but definitely would love suggestions/opinions!

[freddyaboulton]

What's the runtime now? My takeaway is that using grid_resolution=5 can trim the test time to a couple seconds down from like ~10. The next step would be using fewer rows.

[angela97lin]

~30-40 seconds before, 8 seconds after setting grid_resolution to 5 😁

[chukarsten]

Looks good. I think dropping the grid res is a good idea to make it a shorter test.

[freddyaboulton]

Looks good to me @angela97lin !