Correct the description directly below unreleased in CHANGELOG.md.

[Kynea0b]

Summary

PRs under unreleased in CHANGELOG.md should be placed in the h3 hierarchy.

Problem Definition

Currently, the CHANGELOG.md is not organized.
PRs directly under unreleased should be classified as features, improvements, etc. in the h3 hierarchy.
However, they are not classified correctly. Therefore, it needs to be corrected.

Proposal

PRs directly under unreleased should be written in the appropriate location directly under one of the following. :features,improvements, bug fixes,....etc

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For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged (Not decided yet.)
• Contributor assigned/self-assigned (Not decided yet.)

[zemyblue]

Changelog is always updated if the release complete.
And I think this issue is solved by #992 .