Corrected Errors in Post-Grad & Doctorate Graduation Handler

[IllianiCBT]

This PR addresses a small bug that caused errors when personnel were graduating from Education Level 0 (Early Education) academies, and when graduating from Post-Graduate and Doctorate academies.

I also fixed the color of the highlight text used when getting a Master's or Doctorate degree. MekHQ no longer thinks they are negative events.

Closes #4544

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 10.32%. Comparing base (b5ff179) to head (dc9f2d7).
Report is 6 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #4564      +/-   ##
============================================
- Coverage     10.32%   10.32%   -0.01%     
  Complexity     5816     5816              
============================================
  Files           935      935              
  Lines        128792   128798       +6     
  Branches      18951    18949       -2     
============================================
  Hits          13296    13296              
- Misses       114220   114226       +6     
  Partials       1276     1276              

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