Fix artifact initialization dict creation to be recursive

[elronbandel]

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[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (bd53156) 93.91% compared to head (d394d0e) 93.91%.
Report is 1 commits behind head on main.

❗ Current head d394d0e differs from pull request most recent head 84b6c1d. Consider uploading reports for the commit 84b6c1d to get more accurate results

Files	Patch %	Lines
src/unitxt/artifact.py	66.66%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #559   +/-   ##
=======================================
  Coverage   93.91%   93.91%           
=======================================
  Files         213      213           
  Lines        8203     8203           
=======================================
  Hits         7704     7704           
  Misses        499      499           

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