Fix MASE error by passing through y_train

[eccabay]

Closes #4257

[codecov]

Codecov Report

Merging #4258 (1b06f51) into main (30f3242) will increase coverage by 0.1%.
The diff coverage is 100.0%.

@@           Coverage Diff           @@
##            main   #4258     +/-   ##
=======================================
+ Coverage   99.7%   99.7%   +0.1%     
=======================================
  Files        351     351             
  Lines      38497   38512     +15     
=======================================
+ Hits       38376   38391     +15     
  Misses       121     121             

Files Changed	Coverage Δ
...valml/pipelines/time_series_regression_pipeline.py	100.0% <ø> (ø)
evalml/pipelines/binary_classification_pipeline.py	100.0% <100.0%> (ø)
evalml/pipelines/pipeline_base.py	98.5% <100.0%> (ø)
.../pipelines/time_series_classification_pipelines.py	100.0% <100.0%> (ø)
evalml/tests/pipeline_tests/test_pipelines.py	99.9% <100.0%> (+0.1%)	⬆️

[jeremyliweishih]

LGTM