Add changelog entry for PostgreSQL Cidr#change? behavior change

[yahonda]

Motivation / Background

This pull request adds a changelog entry for PostgreSQL Cidr#change? behavior change.

Detail

Follow up #51633

Additional information

None

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Unrelated changes should be opened in separate PRs.
• Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• Tests are added or updated if you fix a bug or add a feature.
• CHANGELOG files are updated for the changed libraries if there is a behavior change or additional feature. Minor bug fixes and documentation changes should not be included.

[yahonda]

It should be merged to 7-2-stable, not main.