Pin qt6 < 6.10.0

[xjules]

Issue
It seems that we need to update RHEL8 to RHEL9 before we can bump qt6
https://www.riverbankcomputing.com/pipermail/pyqt/2025-October/046342.html

(Screenshot of new behavior in GUI if applicable)

• PR title captures the intent of the changes, and is fitting for release notes.
• Added appropriate release note label
• Commit history is consistent and clean, in line with the contribution guidelines.
• Make sure unit tests pass locally after every commit (git rebase -i main --exec 'just rapid-tests')

When applicable

• When there are user facing changes: Updated documentation
• New behavior or changes to existing untested code: Ensured that unit tests are added (See Ground Rules).
• Large PR: Prepare changes in small commits for more convenient review
• Bug fix: Add regression test for the bug
• Bug fix: Add backport label to latest release (format: 'backport release-branch-name')

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.68%. Comparing base (323b5d0) to head (157ed7c).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #12543   +/-   ##
=======================================
  Coverage   90.68%   90.68%           
=======================================
  Files         431      431           
  Lines       29734    29734           
=======================================
  Hits        26963    26963           
  Misses       2771     2771           

Flag	Coverage Δ
cli-tests	37.62% <ø> (ø)
gui-tests	68.75% <ø> (+0.03%)	⬆️
performance-and-unit-tests	74.17% <ø> (-0.02%)	⬇️
test	38.39% <ø> (+0.01%)	⬆️

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[codspeed-hq]

CodSpeed Performance Report

Merging #12543 will not alter performance

_{Comparing xjules:pin_qt_lt_6.10 (157ed7c) with main (323b5d0)}

Summary

✅ 22 untouched

[andreas-el]

💯