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:
web-platform-tests/interop#12 (comment)

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}
NOKEYCHECK=True
GitOrigin-RevId: 86245eb07b2d6a8b90eefb53de3e812f85eab609

blink/web_tests/external/wpt/html/semantics/interactive-elements/the-dialog-element/modal-dialog-scroll-height.html

@@ -27,6 +27,6 @@
 <script>
 test(() => {
   document.querySelector('dialog').showModal();
-  assert_equals(document.scrollingElement.scrollHeight, 600);
+  assert_equals(document.scrollingElement.scrollHeight, window.innerHeight);
 }, 'dialogs should be centered before computing overflow.');
 </script>