The abbreviation "cf." is not properly read in French

### Steps to reproduce

spd-say -l fr cf.

### Obtained behavior

The abbreviation "cf." is read letter by letter "c. f." ([seɛf] in the international phonetic alphabet).

### Expected behavior

The abbreviation "cf." should be read letter "confer" ([kõˈfɛʁ] in the international phonetic alphabet). This is because this abbreviation is very used, well-known (it appears even in the dictionary of the French academy ( https://www.dictionnaire-academie.fr/article/A9C3488-A ) and unambiguous.

### Behavior information

Please follow the next step, to provide us with precious information about how things went wrong on your machine:

* Set `LogLevel` to 5 in your `/etc/speech-dispacher/speechd.conf`
* Restart your computer to make sure it gets taken into account
* Reproduce the issue
* Make a copy of the `speech-dispacher.log` file, it is usually found in `/run/user/1000/speech-dispatcher/log`. Also make a copy of `yourspeechmodule.log` (e.g. `espeak-ng.log`).
* Set `LogLevel` back to 3 in your `/etc/speech-dispacher/speechd.conf`
* Attach the `speech-dispatcher.log` and `yourspeechmodule.log` file to your bug report.
* Also attach your `speechd.conf` file and `yourspeechdmodule.conf` file.

### Distribution
updated Fedora workstation 38

[speech-dispatcher.log](https://github.com/brailcom/speechd/files/11575293/speech-dispatcher.log)
[espeak-ng.log](https://github.com/brailcom/speechd/files/11575303/espeak-ng.log)
[espeak-ng-mbrola.log](https://github.com/brailcom/speechd/files/11575304/espeak-ng-mbrola.log)
### Version of Speech-dispatcher
0.11.4

Start by reproducing `spd-say -l fr cf.` and review the attached `speech-dispatcher.log` and `espeak-ng.log` files to identify where the French abbreviation is handled. Done means the command pronounces `cf.` as “confer” rather than spelling it as “c. f.”.

Written by the indexing model from the issue text.