Fix duplicate license files in msi packages (dotnet#56959)

It appears when we added the workloads subset, the msi projects
contained a step to add a License.txt file to the packages it creates.
This resulted in a conflict as runtime will also add one.

To fix, we'll skip adding the extra License.txt file when the project is
'msi.csproj'.

Fixes dotnet#56516

Directory.Build.targets

@@ -39,7 +39,7 @@
     <None Include="$(LicenseFile)"
           PackagePath="$([System.IO.Path]::GetFileName('$(LicenseFile)'))"
           Pack="true"
-          Condition="'$(MSBuildProjectExtension)' != '.sfxproj'" />
+          Condition="'$(MSBuildProjectExtension)' != '.sfxproj' and '$(MSBuildProjectFile)' != 'msi.csproj'" />
     <None Include="$(PackageThirdPartyNoticesFile)"
           PackagePath="$([System.IO.Path]::GetFileName('$(PackageThirdPartyNoticesFile)'))"
           Pack="true" />