RubyLB: Add a DumpAccessibilityTree testcase

This CL adds a line-broken <ruby> to ruby.html.

Bug: 324111880
Change-Id: I8e638f84278d27f2bd6d0d2062f99677d861b6e6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5612830


Reviewed-by: Aaron Leventhal <aleventhal@chromium.org>
Auto-Submit: Kent Tamura <tkent@chromium.org>
Commit-Queue: Aaron Leventhal <aleventhal@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1312771}