Exclude SOS.NETCore.dll from strong name signing

SOS.NETCore is already fully signed with the open key so we
don't want to try and strong name sign it again. Only authenticode
signing is required.

Author: weshaggard

src/sign.builds

@@ -36,7 +36,7 @@
     native images which causes the signing step to fail for obvious reasons.
   -->
   <ItemGroup>
-    <FilesToSign Include="$(BinDir)*.ni.dll">
+    <FilesToSign Include="$(BinDir)*.ni.dll;$(BinDir)SOS.NETCore.dll">
       <StrongName>None</StrongName>
     </FilesToSign>
   </ItemGroup>