Move Kestrel Sockets tests to their own group (#6869)

Author: Tratcher

src/Servers/Kestrel/test/Sockets.FunctionalTests/Sockets.FunctionalTests.csproj

@@ -5,6 +5,7 @@
     <DefineConstants Condition="$([MSBuild]::IsOSPlatform('OSX'))">$(DefineConstants);MACOS</DefineConstants>
     <DefineConstants>$(DefineConstants);SOCKETS</DefineConstants>
     <ServerGarbageCollection>true</ServerGarbageCollection>
+    <TestGroupName>Sockets.FunctionalTest</TestGroupName>
   </PropertyGroup>
 
   <ItemGroup>