test: fix test_submit_bad_author_email()

[jennifer-richards]

Original test accidentally created a second primary email by trying to modify the PK of an existing Email. That led to a stochastic apparently data-dependent failure that depended on which address was returned by first().

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.58%. Comparing base (306f479) to head (433ff47).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #11186   +/-   ##
=======================================
  Coverage   88.58%   88.58%           
=======================================
  Files         333      333           
  Lines       44662    44669    +7     
=======================================
+ Hits        39565    39572    +7     
  Misses       5097     5097           

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