Fix Vue.config.errorHandler in specs

Description

Changing Vue.config will not work with VTU2, for example

Vue.config.errorHandler = () => {};

The wrapper for VTU 2 is a vue 3 application so it has independent config, so changing global config will not affect it. There is a vue 3 way to do it, but not in VTU 2.

@xanf Could you please provide more context and maybe a recommended approach? I've put here what you've already mentioned in the latest Vue-3 migration call.