Update scroll-timeline-multi-pass.tentative.html

Bug: 1432627
Change-Id: I8728ac267115d0a04410877e09a4369c7ff1eb28
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4520395
Reviewed-by: Anders Hartvoll Ruud <andruud@chromium.org>
Commit-Queue: Kevin Ellis <kevers@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1142662}

scroll-animations/css/scroll-timeline-multi-pass.tentative.html

@@ -18,6 +18,7 @@
   main {
     height: 0px;
     overflow: hidden;
+    scroll-timeline: timeline1 defer, timeline2 defer;
   }
   .scroller {
     height: 100px;
@@ -49,7 +50,7 @@
     function insertScroller(timeline_name) {
       let scroller = document.createElement('div');
       scroller.classList.add('scroller');
-      scroller.style.scrollTimeline = timeline_name;
+      scroller.style.scrollTimeline = `${timeline_name} ancestor`;
       scroller.append(document.createElement('div'));
       main.insertBefore(scroller, element1);
     }