Update GitHub Actions versions to use Node 20

[Alnusjaponica]

Motivation

GitHub official encourages to update GitHub Actions to use Node 20 in their blog posts, as Node 16 has reached its end of life.

Description

We need to

• List up all the files in optuna/ repositories which need updating,
• Carefully examine the change logs of GitHub Actions and describe how updates effects on current CI,

to confirm that it's safe to update these actions before you actually do it. Please refer to #4165 and related PR (e.g. #4208) for reference. Then,

• Update actions/checkout from v3 to v4.
• Update actions/setup-python from v4 to v5.

[HarshitNagpal29]

can you assign this issue to me??

[nzw0301]

@HarshitNagpal29 Thank you for your comment. You can work on this issue since no one is assigned to this issue and https://github.com/optuna/optuna/blob/master/CONTRIBUTING.md does not have such a rule.

[Alnusjaponica]

@nzw0301 Thanks for your comments
@HarshitNagpal29 Thank you for your suggestion. Feel free to work on it. However, please note that we still need to list all the files that need updating and examine how the update affects the current CI in this issue.

[HarshitNagpal29]

However, please note that we still need to list all the files that need updating and examine how the update affects the current CI in this issue.

@Alnusjaponica Ok sir, I will try to do that, I was thinking of updating all the files once and then try to check how each file is behaving, while CI run check.