Fix email settings test in preferences

[gagnieray]

• don't use members administrator's emails if set in preferences, as testing doesn't accept multiple recipients
• use FUI toast message on success

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (3f87dfa) 44.43% compared to head (e6147b3) 44.40%.
Report is 4 commits behind head on develop.

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Additional details and impacted files

@@              Coverage Diff              @@
##             develop     #383      +/-   ##
=============================================
- Coverage      44.43%   44.40%   -0.04%     
  Complexity      5872     5872              
=============================================
  Files            142      142              
  Lines          23866    23824      -42     
=============================================
- Hits           10605    10579      -26     
+ Misses         13261    13245      -16     

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