Add upgrading note for the resource to object migration in ext/sockets

UPGRADING

@@ -459,9 +459,16 @@ PHP 8.0 UPGRADE NOTES
   . ReflectionType::isBuiltin() method has been moved to ReflectionNamedType.
     ReflectionUnionType does not have it.
 
-- Socket:
+- Sockets:
   . The deprecated AI_IDN_ALLOW_UNASSIGNED and AI_IDN_USE_STD3_ASCII_RULES
     flags for socket_addrinfo_lookup() have been removed.
+  . socket_create(), socket_create_listen(), socket_accept(),
+    socket_import_stream(), socket_addrinfo_connect(), socket_addrinfo_bind(),
+    and socket_wsaprotocol_info_import() will now return a Socket object rather
+    than a resource. Return value checks using is_resource() should be replaced
+    with checks for `false`.
+  . socket_addrinfo_lookup() will now return an array of AddressInfo objects
+    rather than resources.
 
 - SPL:
   . SplFileObject::fgetss() has been removed.