Fix for invalid classification accuracy in training

[orhunguley]

Fixes #351

Proposed Changes

• Fixes the invalid accuracy calculation during training.

Checklist

• I have read the CONTRIBUTING guide
• My PR is based from the current GaNDLF master
• Non-breaking change (would not break existing functionality): please provide as many details as possible for any breaking change
• Function/class source code documentation added/updated
• Code has been blacked for style consistency
• If applicable, version information has been updated in GANDLF/version.py
• If adding a git submodule, add to list of exceptions for black styling in pyproject.toml file
• Usage documentation has been updated, if appropriate
• History has been updated, if appropriate
• Tests added or modified to cover the changes; if coverage is reduced, please give explanation
• If customized dependency installation is required (i.e., a separate pip install step is needed for PR to be functional), please ensure it is reflected in all the files that control the CI, namely: python-test.yml, and all docker files [1,2,3,4]

[codecov]

Codecov Report

Merging #361 (2550077) into master (688833a) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #361   +/-   ##
=======================================
  Coverage   90.97%   90.97%           
=======================================
  Files          89       89           
  Lines        4829     4829           
=======================================
  Hits         4393     4393           
  Misses        436      436           

Flag	Coverage Δ
unittests	90.97% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
GANDLF/metrics/regression.py	85.71% <100.00%> (ø)

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