Diminish the severity of renaming ErrorCodes enum members

[A5rocks]

Follow up to #3166, I think breaking is not accurate because ErrorCode is neither exported nor returned anywhere public.

(this is a kind of unnecessary change but I figure better not make people think the next release has what we would consider a breaking change. I'm fine if we decide to keep it as is.)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00000%. Comparing base (8a7674c) to head (d359e70).
Report is 2 commits behind head on main.

Additional details and impacted files

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  Coverage   100.00000%   100.00000%           
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  Files             124          124           
  Lines           18792        18792           
  Branches         1268         1268           
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  Hits            18792        18792