[evaluation] chore: Update azure-ai-evaluation 1.18.0 release date

[kdestin]

Description

Updates the azure-ai-evaluation 1.18.0 release date to Monday, 2026-07-06.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[Copilot]

Pull request overview

This PR updates the azure-ai-evaluation package changelog to align the 1.18.0 release date with the intended Monday release.

Changes:

• Updated the ## 1.18.0 (...) header date in CHANGELOG.md from 2026-07-07 to 2026-07-06.