build(deps): Directory.Packages.props modernized to better address TargetFramework dependent dependencies (#78) [skip ci]

Author: samtrion

Directory.Packages.props

@@ -16,6 +16,7 @@
     <PackageVersion Include="Polyfill" Version="1.34.0" />
     <PackageVersion Include="Verify.Xunit" Version="22.11.2" />
     <PackageVersion Include="xunit" Version="2.6.4" />
-    <PackageVersion Include="xunit.runner.visualstudio" Version="2.4.5" />
+    <PackageVersion Include="xunit.runner.visualstudio" Version="2.5.6" />
+    <PackageVersion Update="xunit.runner.visualstudio" Version="2.4.5" Condition=" '$(TargetFramework)' == 'net5.0' Or '$(TargetFramework)' == 'netcoreapp3.1' " />
   </ItemGroup>
 </Project>