allow for running tests with break on error

[jeking3]

Description

This allows one to run tox -e py39-djmain-sqlite3 -- --pdb and have unit tests break on error into the debugger.

Related Issue

Motivation and Context

How Has This Been Tested?

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 change)

Checklist:

• I have run the make format command to format my code
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have added my name and/or github handle to AUTHORS.rst
• I have added my change to CHANGES.rst
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #890 (843de03) into master (d8e5602) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #890   +/-   ##
=======================================
  Coverage   97.83%   97.83%           
=======================================
  Files          22       22           
  Lines        1062     1062           
  Branches      162      162           
=======================================
  Hits         1039     1039           
  Misses         10       10           
  Partials       13       13           

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[jeking3]

@jazzband/django-simple-history this is a small pull request that improves maintainability; would appreciate a review.

[tim-schilling]

Looks good to me.