Update test libraries

Author: Numpsy

test/Serilog.Enrichers.Environment.Tests/Serilog.Enrichers.Environment.Tests.csproj

@@ -10,9 +10,9 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.8.3" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.7.2" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3" PrivateAssets="all" />
-    <PackageReference Include="xunit" Version="2.4.1" />
+    <PackageReference Include="xunit" Version="2.5.3" />
   </ItemGroup>
 
 </Project>