[ValentinYoushkevich]

Since #2700, mount with attachTo calls app.onUnmount, which only exists since Vue 3.5, so on Vue 3.0–3.4 it throws TypeError: app.onUnmount is not a function (the peer range is vue: 3.x).

// vue 3.4.38, @vue/test-utils 2.5.1
mount(Hello, { attachTo: document.body }) // TypeError: app.onUnmount is not a function

This also breaks every render() of @testing-library/vue on these versions, as it always passes attachTo and depends on @vue/test-utils@^2.4.1.

This uses app.onUnmount when available and otherwise wraps app.unmount, so the container is still removed on unmount. I also ran the whole test suite against Vue 3.4.38: 3 tests fail on main, all pass with this change.

Repro on 2.5.1 with Vue 3.4.38: playground

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