Update dependencies from https://dev.azure.com/dnceng/internal/_git/dotnet-wpf-int build 20200306.12 (#2729)

- Microsoft.DotNet.Wpf.DncEng - 5.0.0-preview.2.20156.12

Co-authored-by: dotnet-maestro[bot] <dotnet-maestro[bot]@users.noreply.github.com>

Author: dotnet-maestro[bot]

eng/Version.Details.xml

@@ -71,9 +71,9 @@
       <Uri>https://github.com/dotnet/corefx</Uri>
       <Sha>8d21b79b924d29088dbde46d42737a657d466b5e</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.DotNet.Wpf.DncEng" Version="5.0.0-preview.2.20156.8">
+    <Dependency Name="Microsoft.DotNet.Wpf.DncEng" Version="5.0.0-preview.2.20156.12">
       <Uri>https://dev.azure.com/dnceng/internal/_git/dotnet-wpf-int</Uri>
-      <Sha>b4b27065f478815d98ffe435645937e2133055cc</Sha>
+      <Sha>b61556bf2f475f1703350e10e4910f34505c426a</Sha>
     </Dependency>
     <Dependency Name="System.IO.Packaging" Version="5.0.0-alpha1.19512.1" CoherentParentDependency="Microsoft.Private.Winforms">
       <Uri>https://github.com/dotnet/corefx</Uri>

eng/Versions.props

@@ -97,6 +97,6 @@
     <SystemReflectionMetadataLoadContextPackage>System.Reflection.MetadataLoadContext</SystemReflectionMetadataLoadContextPackage>
   </PropertyGroup>
   <PropertyGroup>
-    <MicrosoftDotNetWpfDncEngVersion>5.0.0-preview.2.20156.8</MicrosoftDotNetWpfDncEngVersion>
+    <MicrosoftDotNetWpfDncEngVersion>5.0.0-preview.2.20156.12</MicrosoftDotNetWpfDncEngVersion>
   </PropertyGroup>
 </Project>