fix api diff.

build/ApiDiff.props

@@ -7,6 +7,6 @@
     <ItemGroup>
       <PackageDownload Include="$(NugetPackageName)" Version="[$(ApiContractPackageVersion)]" />
       <PackageReference Include="Microsoft.DotNet.ApiCompat" Version="5.0.0-beta.20372.2" PrivateAssets="All" />
-      <ResolvedMatchingContract Include="$(NuGetPackageRoot)\$(NugetPackageName.ToLowerInvariant())\$(ApiContractPackageVersion)\lib\$(TargetFramework)\$(AssemblyName).dll" />
+      <ResolvedMatchingContract Include="$(NuGetPackageRoot)\$(NugetPackageName.ToLowerInvariant())\$(ApiContractPackageVersion)\lib\net461\$(AssemblyName).dll" />
     </ItemGroup>
 </Project>