Tests: silence act() warnings in PublishPanel teardown
The PublishPanel submit/publish handlers are async, which arms React's
act-tracking after the click's act() scope closes. A subsequent bare
root.unmount() then flushes that pending state update outside act() and
logs a "not wrapped in act" warning. Pre-flushing before unmount doesn't
help — the unmount's own flushSync has to run inside act().
Wrap root.unmount() in act() in both clickUpdate and clickPublish. This
also clears two equivalent warnings that already existed via clickUpdate
before the publish-success-pill work added clickPublish.