This integration test is currently the only one that spawns a separate
browser instance. However, while it closes the browser once it's done,
it doesn't close the page (and therefore doesn't call the `testingClose`
method) like the other integration tests do.
This commit fixes this difference by closing the page before closing the
browser, thereby ensuring all regular cleanup logic gets called and we
avoid (intermittent) shutdown tracebacks in the logs. This allows
upcoming integration tests that spawn a separate browser instance to
reuse this pattern to cleanly end the test.
Given that we integrate the `closeSinglePage` code from #17962 for this
patch, @calixteman is credited as the co-author.
Co-authored-by: Calixte Denizet <calixte.denizet@gmail.com>
f4053c2b3e