Remove the version constraint on blackdoc #6146
Description
Motivation
blackdoc 0.3.10 was released yesterday, causing the checks workflow to fail.
*
- https://pypi.org/project/blackdoc/#history
- https://github.com/optuna/optuna/actions/runs/15572122231/job/43850030515
I opened a PR to add the version constraint, blackdoc<0.3.10, as a hotfix. This issue suggests fixing the above error and remove the version constraint.
Suggestion
Remove the version constraint added at #6145.
Additional context (optional)
No response