Set upper constraint for Optuna

[himkt]

What this PR does / why we need it:

This PR introduces an upper version constraint for Optuna.
Please refer to #1851 for the background.

Which issue(s) this PR fixes:
Related #1851

Checklist:

• Docs included if any changes are user facing => no user-faceing change

[aws-kf-ci-bot]

Hi @himkt. Thanks for your PR.

I'm waiting for a kubeflow member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[Arhell]

/ok-to-test

[tenzen-y]

Thanks for creating the PR @himkt !

@kubeflow/wg-automl-leads Could you approve workflows in Github Action?

[coveralls]

Coverage decreased (-0.3%) to 73.93% when pulling 352a6db on himkt:optuna-version-constraint into 7f1afbd on kubeflow:master.

[tenzen-y]

/lgtm

[johnugeorge]

/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: himkt, johnugeorge

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