PY39: Support pre-__or__ types

[effigies]

I'm honestly not sure why this isn't causing the current tests to fail, but it does cause sdcflows tests to fail: https://github.com/nipreps/sdcflows/actions/runs/10890546744/job/30219507551

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.76%. Comparing base (5aa2473) to head (94ec119).
Report is 9 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #223   +/-   ##
=======================================
  Coverage   94.76%   94.76%           
=======================================
  Files          15       15           
  Lines        1756     1756           
  Branches      328      328           
=======================================
  Hits         1664     1664           
  Misses         76       76           
  Partials       16       16           

Flag	Coverage Δ
unittests	94.76% <100.00%> (ø)

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