Remove warnings during build and ignore built artifacts.

[leander-dsouza]

Description of contribution in a few bullet points

• Official Python packaging documentation now recommends using SPDX expressions instead of Trove's classifiers, and resolves the following warning:

  dist.py:759: SetuptoolsDeprecationWarning: License classifiers are deprecated.
  !!
  
          ********************************************************************************
          Please consider removing the following classifiers in favor of a SPDX license expression:
  
          License :: OSI Approved :: MIT License
  
          See https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license for details.
          ********************************************************************************
  !!
  

• Added ignores for the dist/ directory to avoid built artifacts from registering as commits.

Description of how this change was tested

• No warnings when invoking python3 -m build.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (983c232) to head (3688b1b).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@          Coverage Diff           @@
##           master     #53   +/-   ##
======================================
  Coverage    0.00%   0.00%           
======================================
  Files          11      11           
  Lines         551     551           
======================================
  Misses        551     551           

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[cottsay]

I added a leading slash to the .gitignore and set the license expression to use SPDX since the classifier is being removed.

Thanks!