Add a comment in eri.py about a possible error this can catch

[billsacks]

Description

This was motivated by the discussion in #4859 . I realized that the ERI test can catch the type of error that the ERS2 was designed to catch - where the mere act of writing a restart file can lead to an answer change. I thought it was worth mentioning this, both so care is taken to maintain the ability of the ERI test to catch this kind of error, and to give some guidance for people who run into a failure in this comparison suggesting this possible cause.

Checklist

• My code follows the style guidelines of this project (black formatting)
• I have performed a self-review of my own code
• My changes generate no new warnings
• I have added tests that exercise my feature/fix and existing tests continue to pass
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding additions and changes to the documentation

[billsacks]

I wasn't sure where the best place would be to put this comment to give the best chance that someone will actually find it when they need it, so I welcome input on a better place to put it - as well as any comments to help clarify the wording.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 28.29%. Comparing base (3c0d623) to head (28fe4b5).
⚠️ Report is 166 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4959      +/-   ##
==========================================
- Coverage   28.32%   28.29%   -0.04%     
==========================================
  Files         262      262              
  Lines       38340    38384      +44     
  Branches     8114     8126      +12     
==========================================
  Hits        10860    10860              
- Misses      26234    26276      +42     
- Partials     1246     1248       +2     

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[mnlevy1981]

What would you think about putting the comment in the test-type table on the system testing doc page? I think my preference would be to include it both in eri.py and in the documentation, though I'm always a little concerned about duplicating documentation and then in the future things get out of sync... that doesn't seem likely in this case, hence my thinking that it could go in both places.

[billsacks]

@mnlevy1981 - good idea, thanks. I have made that change.

[mnlevy1981]

This looks good to me - I like that you put this note in the case (Suffix branch) section of the description. I was expecting it at the bottom of the cell, and was confused when I couldn't find it until I realized how the rest of the cell was organized :)