[css-contain-2] Fix reference to HTML algo step, since it moved.

Author: tabatkins

css-contain-2/Overview.bs

@@ -1466,14 +1466,16 @@ Restrictions and Clarifications {#cv-notes}
 	after the requestAnimationFrame callbacks
 	of the frame that renders the effects of the change
 	have run.
-	Specifically, such changes will take effect right after
-	step 11 of <a href="https://html.spec.whatwg.org/multipage/webappapis.html#update-the-rendering">Update the Rendering</a> step of the Processing Model.
+	Specifically, such changes will take effect between steps 12 and 13
+	of <a href="https://html.spec.whatwg.org/multipage/webappapis.html#update-the-rendering">Update the Rendering</a> step of the Processing Model
+	(between [=run the animation frame callbacks=]
+	and [=run the update intersection observations steps=]).
 
 	<div class=note>
 		Determining the viewport intersection of the element
 		can be done with an internal version of an IntersectionObserver.
 		However, since the observations from this are dispatched at
-		step 12 of Update the Rendering,
+		step 13 of Update the Rendering,
 		any changes to the [=skipped contents|skipped=] (and thus painted) state
 		will not be visible to the user until the next frame's processing.
 		For this reason, updating the [=skipped contents|skipped=] state,