Convert .travis.yml to a GitHub Actions workflow

[jwodder]

Closes #139.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.56%. Comparing base (857ada2) to head (32b3bd9).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #140   +/-   ##
=======================================
  Coverage   77.56%   77.56%           
=======================================
  Files          60       60           
  Lines        4720     4720           
  Branches      956      956           
=======================================
  Hits         3661     3661           
  Misses        895      895           
  Partials      164      164           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[yarikoptic]

Great, thank you @jwodder