sandboxjs: make node image discovery more robust

[mr-c]

docker images strips out the "docker.io" registry, so change our query to match

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 34.33%. Comparing base (197eac9) to head (5713417).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #359   +/-   ##
=======================================
  Coverage   34.33%   34.33%           
=======================================
  Files          30       30           
  Lines       35362    35362           
  Branches     9553     9553           
=======================================
  Hits        12142    12142           
  Misses      20327    20327           
  Partials     2893     2893           

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