Merge pull request optuna#2566 from HideakiImamura/release-v2.7.0

Bump up version to v2.7.0

Merge pull request optuna#2445 from hvy/bump-version-260

Bump `release-v2.6.0` version `2.6.0`

Merge pull request optuna#2282 from HideakiImamura/bump-up-v2.5.0

Bump up version number to v2.5.0

Merge pull request optuna#2188 from HideakiImamura/2187-backport

[Backport] Fix the syntax of `pypi-publish.yml`

Merge pull request optuna#1978 from toshihikoyanase/add-rdb-support-t…

…o-motpe

Add RDB support to `MoTPEMultiObjectiveSampler`

Merge pull request optuna#1886 from hvy/bump-to-v2.2.0

Bump to v2.2.0

Merge pull request optuna#1790 from hvy/fix-fanova-int-log-uniform

[Backport] Fix fANOVA for `IntLogUniformDistribution`

Merge pull request optuna#1561 from hvy/bp-1551

[Backport] Add `packaging` in install_requires.

Merge pull request optuna#1476 from toshihikoyanase/bump-to-v2.0.0rc0

Bump up version to `2.0.0rc0`.

Merge pull request optuna#1313 from toshihikoyanase/release-v1.5.0

Apply optuna#1291 and optuna#1306 to the `release-v1.5.0`.