Fix double single quotes in `connect` error print

(cherry picked from commit 4950ef7478315cfcf27e12f0d3c0a034bd66cf92)

core/object.cpp

@@ -1363,7 +1363,7 @@ Error Object::connect(const StringName &p_signal, Object *p_to_object, const Str
 
 	Signal::Target target(p_to_object->get_instance_ID(), p_to_method);
 	if (s->slot_map.has(target)) {
-		ERR_EXPLAIN("Signal '" + p_signal + "'' already connected to given method '" + p_to_method + "' in that object.");
+		ERR_EXPLAIN("Signal '" + p_signal + "' is already connected to given method '" + p_to_method + "' in that object.");
 		ERR_FAIL_COND_V(s->slot_map.has(target), ERR_INVALID_PARAMETER);
 	}