generate.py: reformat for black 2026.1.0

[ctz]

Fixing CI - https://github.com/rustls/webpki/actions/runs/21111210276

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.78%. Comparing base (c4d5b19) to head (16c85af).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #438   +/-   ##
=======================================
  Coverage   96.78%   96.78%           
=======================================
  Files          19       19           
  Lines        3797     3797           
=======================================
  Hits         3675     3675           
  Misses        122      122           

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