Changes to fix Windows runner CI jobs
The previous method of installer the SDK for the version of .NET that we want to run is not working with the new Windows CI runner image. It appears that as .NET 8 is now the default, all the tests are run with that version, and if the runtime is not installed then the SDK cannot run the tests targeting that specific runtime.
These changes make the test job more robust as it will always use the installed LTS version of the SDK for the test runner but it installs the specific runtime required for the test run and runs the tests targeting that runtime.