merge_checker vcpkg tests are a bit useless

[cmannett85]

They test the previously released version package stored in the remote package repos, which is fine but has no bearing on the code being merged into main which is the whole point of the GHA. Investigate having the updated packages locally generated by a script (which is checked in) and then tested, this will also simplify the release process because the updated packages can be generated automatically before pushing upstream.