Avoid passing floating point values to WebDriver's wheel action in overscroll-behavior-root.html.

Differential Revision: https://phabricator.services.mozilla.com/D241765

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1954403
gecko-commit: 8b5352b76dea6f0fbede86e7386022439464f590
gecko-reviewers: botond

Author: hiikezoe

css/css-overscroll-behavior/overscroll-behavior-root.html

@@ -29,7 +29,8 @@
   assert_not_equals(originalScrollPos, 0, "Should have scrolled to get the iframe into view");
 
   await new test_driver.Actions()
-    .scroll(bounds.left + bounds.width / 2, bounds.top + bounds.height / 2, 0, -100)
+    .scroll(Math.round(bounds.left + bounds.width / 2),
+            Math.round(bounds.top + bounds.height / 2), 0, -100)
     .send();
 
   assert_equals(window.scrollY, originalScrollPos, "overscroll-behavior should work on the root");