Merge pull request optuna#3458 from himkt/bump-v3.0.0-b0

Bump Optuna to v3.0.0-b0

Merge pull request optuna#3303 from HideakiImamura/backport-v3.0.0-a2

[Backport] Allow fail_state_trials show warning when heartbeat is enabled

Merge pull request optuna#3288 from HideakiImamura/update-3.0.0-a1

Upgrade version number to v3.0.0a1

Merge pull request optuna#3141 from HideakiImamura/bump-up-version-to…

…-3.0.0a0

Bump up version to v3.0.0a0

Merge pull request optuna#2975 from HideakiImamura/bump-up-version-2.10

Bump up version to 2.10

Merge pull request optuna#2839 from hvy/bump-to-v2.9.1

Bump to v2.9.1

Merge pull request optuna#2828 from hvy/bump-to-v2.9.0

Bump to v2.9.0

Merge pull request optuna#2728 from hvy/gp-2717

Backport of optuna#2717

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`