Fix 3.12 ET and datetime deprecation warnings

[JSCU-CNI]

This PR, together with fox-it/flow.record#136 should fix all pytest deprecation warnings when running CPython 3.12.

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 75.52%. Comparing base (85082d4) to head (6ffae3e).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
dissect/target/plugins/os/windows/adpolicy.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #842      +/-   ##
==========================================
- Coverage   75.52%   75.52%   -0.01%     
==========================================
  Files         305      305              
  Lines       26362    26363       +1     
==========================================
  Hits        19911    19911              
- Misses       6451     6452       +1     

Flag	Coverage Δ
unittests	75.52% <85.71%> (-0.01%)	⬇️

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