[BUGFIX] Fix output sanitization type checking

[jmbannon]

In the inspection output, we check function's return types via issubclass to see if an optimization can be made. Guard against this check in case the return type isn't a class -- it could be a Union[..., ...] from a conditional.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.36%. Comparing base (b195f37) to head (4e060a2).
⚠️ Report is 7 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1467   +/-   ##
=======================================
  Coverage   92.35%   92.36%           
=======================================
  Files         117      117           
  Lines        7734     7736    +2     
=======================================
+ Hits         7143     7145    +2     
  Misses        591      591           

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