Enable `<RollForward>major</RollForward>` for `ILSpy.exe`

Allow `ILSpy.exe` to run when .NET 8 (the version it currently targets)
is not installed, but a later major version, e.g. .NET 9, is available.

ref. https://learn.microsoft.com/en-us/dotnet/core/versions/selection#control-roll-forward-behavior

ref. https://github.com/icsharpcode/ILSpy/issues/3390

ILSpy/ILSpy.csproj

@@ -3,6 +3,7 @@
   <PropertyGroup>
     <OutputType>WinExe</OutputType>
     <TargetFramework>net8.0-windows</TargetFramework>
+    <RollForward>major</RollForward>
     <RuntimeIdentifiers>win-x64;win-arm64</RuntimeIdentifiers>
     <GenerateAssemblyInfo>False</GenerateAssemblyInfo>
     <AutoGenerateBindingRedirects>false</AutoGenerateBindingRedirects>