[scroll-animations-1] Clarify that timeline identity is also not cycled.

See #7759 (comment)

Author: fantasai

scroll-animations-1/Overview.bs

@@ -922,9 +922,10 @@ spec: cssom-view-1; type: dfn;
 	through those APIs.
 
 	If the final style and layout update
-	would result in a change of time for any [=scroll progress timelines=] or
-	[=view progress timelines=], they will not be re-sampled to reflect the
-	new offset until the next update of the rendering.
+	would result in a change in the time or scope (see 'timeline-scope')
+	of any [=scroll progress timelines=] or [=view progress timelines=],
+	they will not be re-sampled to reflect the new state
+	until the next update of the rendering.
 
 	Nothing in this section is intended to require
 	that scrolling block on layout or script.