Ensure that version in vcpkg.json and AzureVcpkg.cmake are the same

Dependabot opens updates to vcpkg.json but has no way of updating AzureVcpkg.cmake. When the two values diverge it can result in bad build behavior.

Two possible fixes:

* Have AzureVcpkg.cmake read the value from vcpkg.json (requires upgrading minimum cmake version to 3.19) OR
* Have some kind of additional check that fails if the values in those files differ OR
* A GitHub Action (or some kind of automation) that updates PRs opened by dependabot when it makes sense to do so