ci: fix miri checks

[aborgna-q]

Fixes #1650

Manual run: https://github.com/CQCL/hugr/actions/runs/11815871369/job/32917969928

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.50%. Comparing base (935c61b) to head (1f22cc9).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1651   +/-   ##
=======================================
  Coverage   85.50%   85.50%           
=======================================
  Files         136      136           
  Lines       25252    25252           
  Branches    22164    22164           
=======================================
  Hits        21592    21592           
  Misses       2456     2456           
  Partials     1204     1204           

Flag	Coverage Δ
python	92.42% <ø> (ø)
rust	84.54% <ø> (ø)

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