Update OpenAI package version to 2.7.0 and fix typo in project file

[aasimkhan30]

Description

A typo in (<ackageReference> instead of <PackageReference>) caused the OpenAI package to never be directly referenced. MSBuild silently ignored the malformed element, so the OpenAI version specified in Packages.props was never applied — NuGet resolved it purely from transitive dependencies instead.

Code Changes Checklist

• New or updated unit tests added
• All existing tests pass (dotnet test)
• Code follows contributing guidelines
• Logging/telemetry updated if relevant
• No protocol or behavioral regressions

Reviewers: Please read our reviewer guidelines

[github-actions]

As part of updating the dependencies in Packages.props we require that any PRs opened also verify that
they've done the following checks.

Please respond to this comment verifying that you've done the appropriate validation (or explain why it's not necessary) before merging in the PR

• Built and tested the change locally to validate that the update doesn't cause any regressions and fixes the issues intended
• Tested changes on all major platforms
  • Windows
  • Linux
  • Mac
• Check the source repo for any open issues with the release being updated to (if available)