espeak-ng-mbrola doesn't default to mbrola voices

[sthibaul]

Steps to reproduce

spd-say -o espeak-ng-mbrola a

Obtained behavior

This is speaking with an espeak voice, not mbrola voice.

Expected behavior

It should select an appropriate mbrola voice.

Behavior information

The espeak-ng-mbrola.log file shows

 Mon Apr  1 16:50:22 2024 [146104]: Espeak-ng: Requested data: |<speak>a</speak>| 0 16
 Mon Apr  1 16:50:22 2024 [146107]: Espeak-ng: set_language_and_voice fr-fr 1
 Mon Apr  1 16:50:22 2024 [146221]: Espeak-ng: Successfully set voice to "fr-fr"
 Mon Apr  1 16:50:22 2024 [146225]: Espeak-ng: set_language_and_voice fr-fr 1
 Mon Apr  1 16:50:22 2024 [146291]: Espeak-ng: Successfully set voice to "fr-fr"

Probably we are simply not telling at all the espeak_SetVoiceByProperties call to use mbrola voices.