Make throwing errors in setup-dotnet more informative

[IvanZosimov]

Description: During the installation of .NET using the setup-dotnet action some errors may be thrown. Usually, an error message should contain a comprehensive reason for the error, but in the setup-dotnet, there is a case where it's not like that. These lines of code contain a small bug that should be fixed.

Related issue: Link

Check list:

• [ ] Mark if documentation changes are required.
• [ ] Mark if tests were added or updated to cover the changes.