Don't "persist_amounts" in order recalculation

[jarednorman]

This association is autosaved, and Rails knows not to retouch things when autosaving associated records. I did a test to confirm that removing this doesn't change whether the field is persisted.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.66%. Comparing base (9956911) to head (736babe).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6451      +/-   ##
==========================================
- Coverage   89.66%   89.66%   -0.01%     
==========================================
  Files         990      990              
  Lines       20793    20792       -1     
==========================================
- Hits        18645    18644       -1     
  Misses       2148     2148              

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[mamhoff]

This needs a rebase :)