Add changelog entry for #3466

[mbg]

Probably worth adding before the next release.

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.

Which use cases does this change impact?

Environments:

• Testing/None - This change does not impact any CodeQL workflows in production.

How did/will you validate this change?

• None - I am not validating these changes.

If something goes wrong after this change is released, what are the mitigation and rollback strategies?

• Rollback - Change can only be disabled by rolling back the release or releasing a new version with a fix.

How will you know if something goes wrong after this change is released?

N/A

Are there any special considerations for merging or releasing this change?

• Special considerations - This change should only be merged once certain preconditions are met. Please provide details of those or link to this PR from an internal issue.

Should be merged before the next release.

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

Updates the repository changelog to capture a previously merged/related user-facing change (#3466) so it’s included in the next release notes.

Changes:

• Replaces the “[UNRELEASED]” placeholder “No user facing changes.” with a bullet describing experimental support for testing connections to private package registries.
• Adds a link to the relevant documentation and PR reference (#3466).