Refactor varying your earnings test

[anth-volk]

Fixes #2692

Refactors the varying your earnings test to better serve as an integration test by:

• Correctly coding fixtures
• Removing duplicative fixtures that divorce the test from the context it's testing
• Running only one sim instead of three, a holdover from the original purpose of this test that is no longer necessary

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.60%. Comparing base (0d41b7b) to head (aca4b07).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2694      +/-   ##
==========================================
- Coverage   81.23%   80.60%   -0.63%     
==========================================
  Files          49       49              
  Lines        1609     1609              
  Branches      208      208              
==========================================
- Hits         1307     1297      -10     
- Misses        254      264      +10     
  Partials       48       48              

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