Add Downgrade CI

[ChrisRackauckas]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.71%. Comparing base (bda0548) to head (ce4d7c5).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #464   +/-   ##
=======================================
  Coverage   62.71%   62.71%           
=======================================
  Files          12       12           
  Lines         574      574           
=======================================
  Hits          360      360           
  Misses        214      214           

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