Drive-by clean-ups

[nedbat]

• removed Jira webhook code, since we don't expect to have Jira-initiated actions.
• pylint violations
• moved tests into the tests/ directory and consolidated to match the .py files
• move an if into a match/case

[codecov]

Codecov Report

Patch coverage: 97.61% and project coverage change: +3.34% 🎉

Comparison is base (bce4b0f) 80.36% compared to head (26d3b5c) 83.71%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #264      +/-   ##
==========================================
+ Coverage   80.36%   83.71%   +3.34%     
==========================================
  Files          41       38       -3     
  Lines        3082     2916     -166     
  Branches      328      306      -22     
==========================================
- Hits         2477     2441      -36     
+ Misses        572      442     -130     
  Partials       33       33              

Files Changed	Coverage Δ
openedx_webhooks/__init__.py	74.60% <ø> (-0.79%)	⬇️
openedx_webhooks/github_views.py	27.52% <0.00%> (+0.25%)	⬆️
openedx_webhooks/tasks/__init__.py	51.61% <ø> (-4.27%)	⬇️
tests/test_utils.py	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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