Update TargetPlatformVersion to use WindowsSDKVersion

Author: DefaultRyan

test/nuget/TestRuntimeComponentCSharp/TestRuntimeComponentCSharp.csproj

@@ -11,7 +11,7 @@
     <AssemblyName>TestRuntimeComponentCSharp</AssemblyName>
     <DefaultLanguage>en-US</DefaultLanguage>
     <TargetPlatformIdentifier>UAP</TargetPlatformIdentifier>
-    <TargetPlatformVersion Condition=" '$(TargetPlatformVersion)' == '' ">10.0</TargetPlatformVersion>
+    <TargetPlatformVersion Condition=" '$(TargetPlatformVersion)' == '' ">$(WindowsSDKVersion)</TargetPlatformVersion>
     <TargetPlatformMinVersion>10.0.18362.0</TargetPlatformMinVersion>
     <MinimumVisualStudioVersion>14</MinimumVisualStudioVersion>
     <FileAlignment>512</FileAlignment>