Fix mapping of event listener codes to APScheduler event classes

[jcass77]

Fixes #98.

[codecov-commenter]

Codecov Report

Merging #99 into master will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #99      +/-   ##
==========================================
+ Coverage   96.56%   96.57%   +0.01%     
==========================================
  Files           6        6              
  Lines         262      263       +1     
==========================================
+ Hits          253      254       +1     
  Misses          9        9              

Impacted Files	Coverage Δ
django_apscheduler/jobstores.py	97.01% <100.00%> (+0.02%)	⬆️

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