Fix modal-dialog-scroll-height.html

This test is failing in all browsers on wpt.fyi due to the hard coded
height:
https://wpt.fyi/results/html/semantics/interactive-elements/the-dialog-element/modal-dialog-scroll-height.html

I'm not sure why it passes in the chromium test infrastructure, but
people want to remove it:
https://github.com/web-platform-tests/interop-2022/issues/12#issuecomment-1009154280

This patch replaces the hard coded height with window.innerHeight.

Change-Id: If27a4b07ca235190d19cbe2f52bbfe6dd2594225
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3379191


Auto-Submit: Joey Arhar <jarhar@chromium.org>
Reviewed-by: Steve Kobes <skobes@chromium.org>
Commit-Queue: Steve Kobes <skobes@chromium.org>
Cr-Commit-Position: refs/heads/main@{#958207}