[SL.Core] Update Moq & xunit

tests/SixLabors.Core.Tests/SixLabors.Core.Tests.csproj

@@ -28,10 +28,10 @@
 
   <ItemGroup>
     <PackageReference Include="StyleCop.Analyzers" Version="1.1.0-beta004" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.0.0" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.2.0" />
-    <PackageReference Include="xunit" Version="2.2.0" />
-    <PackageReference Include="Moq" Version="4.7.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.8.0" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.0" />
+    <PackageReference Include="xunit" Version="2.4.0" />
+    <PackageReference Include="Moq" Version="4.9.0" />
   </ItemGroup>
 
   <ItemGroup>