[scroll-animations] Modernize at-scroll-timeline-multi-pass...html

Bug: 1317765
Change-Id: Ib7417a7cbebf1db075401f80a5a9f1e1ae7a1d8d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3859329


Reviewed-by: Robert Flack <flackr@chromium.org>
Commit-Queue: Anders Hartvoll Ruud <andruud@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1040967}