Don't pack the sample

Microsoft.Toolkit.Uwp.Samples.BackgroundTasks/Microsoft.Toolkit.Uwp.Samples.BackgroundTasks.csproj

@@ -17,6 +17,7 @@
     <FileAlignment>512</FileAlignment>
     <ProjectTypeGuids>{A5A43C5B-DE2A-4C0C-9213-0A381AF9435A};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
     <AllowCrossPlatformRetargeting>false</AllowCrossPlatformRetargeting>
+    <IsPackable>false</IsPackable>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <PlatformTarget>AnyCPU</PlatformTarget>