Admin: Skip pytest 9.0.0

[bblommers]

Fixes the build, as that's currently broken with pytest==9.0.0.

This is already fixed in pytest main, so I expect this to work again with 9.0.1.

Supercedes #9459

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.02%. Comparing base (4b18f32) to head (4738a63).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #9460   +/-   ##
=======================================
  Coverage   93.02%   93.02%           
=======================================
  Files        1293     1293           
  Lines      116181   116181           
=======================================
  Hits       108081   108081           
  Misses       8100     8100           

Flag	Coverage Δ
servertests	28.82% <ø> (ø)
unittests	93.00% <ø> (ø)

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