LUCENE-9950: move changes entry for backport to 8.9

[gsmiller]

Description

I've posted a separate PR to backport the LUCENE-9950 work into 8.9. If we move forward with that, we should update the CHANGES.txt entry.

Solution

Just move the CHANGE.txt entry under 8.9.

Tests

N/A

Checklist

Please review the following and check all that apply:

• I have reviewed the guidelines for How to Contribute and my code conforms to the standards described there to the best of my ability.
• I have created a Jira issue and added the issue ID to my pull request title.
• I have given Lucene maintainers access to contribute to my PR branch. (optional but recommended)
• I have developed this patch against the main branch.
• I have run ./gradlew check.
• I have added tests for my changes.

[mikemccand]

Thanks @gmiller!