Fix tabular classifier serve

[ethanwharris]

What does this PR do?

Fixes flash serve with the tabular classifier checkpoint

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[codecov]

Codecov Report

Merging #1324 (5144afd) into master (7facf06) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1324   +/-   ##
=======================================
  Coverage   91.66%   91.66%           
=======================================
  Files         287      287           
  Lines       12833    12843   +10     
=======================================
+ Hits        11763    11773   +10     
  Misses       1070     1070           

Flag	Coverage Δ
unittests	91.66% <100.00%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
flash/tabular/classification/model.py	97.36% <100.00%> (+0.39%)	⬆️
flash/tabular/regression/model.py	100.00% <100.00%> (ø)

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