chore: add .jj to .gitignore

[drmorr0]

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Description

Please describe what this PR does

Testing done

• How did you test your changes?
• Does this code require any new tests to be written?

Additional info

Resolves #xxxx

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.91%. Comparing base (7a81987) to head (940a69f).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #169   +/-   ##
=======================================
  Coverage   72.91%   72.91%           
=======================================
  Files          56       56           
  Lines        3020     3020           
=======================================
  Hits         2202     2202           
  Misses        818      818           

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