[Workloads] Fix license and icon paths in msi proj

[pjcollins]

I was running into a couple of issues when building msi.csproj files
generated by the GenerateVisualStudioWorkload task:

C:\Program Files\dotnet\sdk\5.0.301\Sdks\NuGet.Build.Tasks.Pack\build\NuGet.Build.Tasks.Pack.targets(221,5): error : Could not find a part of the path 'C:\Users\peter\source\yaml-templates\nuget-msi-convert\msbuild\obj\Debug\src\msiPackage\x86\Microsoft.Android.Sdk.Windows\obj\Debug\src\msiPackage\x86\Microsoft.Android.Sdk.Windows'.

C:\Program Files\dotnet\sdk\5.0.301\Sdks\NuGet.Build.Tasks.Pack\build\NuGet.Build.Tasks.Pack.targets(221,5): error NU5046: The icon file 'Icon.png' does not exist in the package.

The first error was a result of the following relative path being
included in the LICENSE.TXT item:

<None Include="obj\Debug\src\msiPackage\x86\Microsoft.Android.Sdk.Windows\LICENSE.TXT" Pack="true" PackagePath="\" />

Since LICENSE.TXT is created in the same directory as msi.proj, we
can exclude this relative path.

The second error appears to be a result of a missing Icon.png item,
which has been added.

The generated pack item content should now look like this:

<ItemGroup>
  <None Include="C:\Users\peter\source\yaml-templates\nuget-msi-convert\msbuild\bin\Microsoft.Android.Sdk.Windows.30.0.100-ci.main.61-x86.msi" Pack="true" PackagePath="\data" />
  <None Include="C:\Users\peter\source\yaml-templates\nuget-msi-convert\msbuild\bin\Microsoft.Android.Sdk.Windows.30.0.100-ci.main.61-x86.json" Pack="true" PackagePath="\data\msi.json" />
  <None Include="Icon.png" Pack="true" PackagePath="" />
  <None Include="LICENSE.TXT" Pack="true" PackagePath="\" />
</ItemGroup>