If restore fails, CI script should exit with an error

[mattchenderson]

Version

N/A

Description

In check-vulnerabilities.ps1, we should probably capture the exit code from the dotnet restore command and possibly throw an error before we get to the package listing operation. If restore fails partially, the package listing can git tripped on versions in dependencies not getting snapped forward properly.

Steps to reproduce

This was encountered with early iterations of #3780, as the package was not on the feed.