prevent scroll when resetting page focus (#4065)

[timothycohen]

Fixes #4065. While resetting focus, Safari was scrolling over the top margin.

As it’s a Safari specific issue, the change in test from fail to pass is only visible when running Playwright with WebKit.

This is my first PR, so let me know if I missed something in the workflow, thanks!

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Latest commit: 30ad83c

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[Rich-Harris]

excellent, thank you!