docker: don't run as root

[keeakita]

Attempt to use a non-root user for the Docker image.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.37%. Comparing base (ec189a2) to head (94eb7c4).
Report is 71 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #284   +/-   ##
=======================================
  Coverage   84.37%   84.37%           
=======================================
  Files          20       20           
  Lines        3756     3756           
=======================================
  Hits         3169     3169           
  Misses        587      587           

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[john-z-yang]

This looks good to me, thank you so much!