[Bug] Change test domain from *.jupyter.com/* to *.jupyter.org/*

[Sync271]

Closes #852
Chose to go with jupyter.org over example.com because event.mock.jupyter.org/message felt like it makes more sense.
Let me know if you guys think otherwise and I'll be happy to change.

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[codecov-commenter]

Codecov Report

Merging #853 (2455944) into main (7a0080c) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #853   +/-   ##
=======================================
  Coverage   70.12%   70.12%           
=======================================
  Files          65       65           
  Lines        7621     7621           
  Branches     1268     1268           
=======================================
  Hits         5344     5344           
  Misses       1895     1895           
  Partials      382      382           

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[Zsailer]

Thanks!

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