add black check workflow

[epassaro]

Description

A simple action to run black --check tardis on every push to a PR.

Motivation and Context

Enforce PEP8.

How Has This Been Tested?

• Testing pipeline
• Other (please describe)

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• None of the above (please describe)

Checklist:

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have built the documentation on my fork following these instructions
• I have assigned and requested two reviewers for this pull request

[codecov]

Codecov Report

Merging #1398 (dabe080) into master (e8ef961) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1398   +/-   ##
=======================================
  Coverage   70.04%   70.04%           
=======================================
  Files          67       67           
  Lines        5312     5312           
=======================================
  Hits         3721     3721           
  Misses       1591     1591           

Impacted Files	Coverage Δ
tardis/tardis/widgets/tests/test_shell_info.py	100.00% <0.00%> (ø)

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[jaladh-singhal]

@epassaro thank you for making this - it was very necessary!