fix: add missing deepcopy func

[eddycharly]

Explanation

Add missing deepcopy func.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 7 lines in your changes missing coverage. Please review.

Project coverage is 24.56%. Comparing base (2389f3a) to head (2f5ca76).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/apis/policy/v1alpha1/assertion_tree.go	0.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #524      +/-   ##
==========================================
- Coverage   24.60%   24.56%   -0.04%     
==========================================
  Files          92       92              
  Lines        4337     4344       +7     
==========================================
  Hits         1067     1067              
- Misses       3160     3167       +7     
  Partials      110      110              

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