plugin XEP-0234: fix action type when pre-flight file confirmation is confirmed: the `C.META_TYPE_FILE` can't be used in this case as it is a preflight and we don't have yet data such as progress ID. `C.META_TYPE_FILE` is used as a sub-type to help with dialog management in frontend.

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−this certificates are used to enable TLS during tests. Those must be the same as in
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−backend_e2e (they are generated there)