Add retroactive changelog note for #3054

[henrymercer]

Risk assessment

For internal use only. Please select the risk level of this change:

• Low risk: Changes are fully under feature flags, or have been fully tested and validated in pre-production environments and are highly observable, or are documentation or test only.

Merge / deployment checklist

• Confirm this change is backwards compatible with existing workflows.
• Consider adding a changelog entry for this change.
• Confirm the readme and docs have been updated if necessary.

[Copilot]

Pull Request Overview

This PR adds a retroactive changelog entry for pull request #3054, which improved CodeQL Action performance by reducing its size and speeding up workflows by approximately 4 seconds. The change updates the 3.30.0 release notes to replace "No user facing changes" with a proper description of the performance improvement.

• Adds changelog entry for PR #3054 to version 3.30.0
• Replaces placeholder text with meaningful user-facing change description