bug#47672: owncloud-client : "Could not read system exclude file"

[Fulbert]

Hello !

After setting up an account to a davs server, the synchronisation
fails with messages :

* On the GUI : "Could not read system exclude file"

* In log file :
20210409_1235_owncloud.log.0.gz:04-09 12:35:55:294 [ info sync.configfile ]:    
Adding system ignore list to csync: 
"/home/fulbert/etc/ownCloud/sync-exclude.lst"
20210409_1235_owncloud.log.0.gz:04-09 12:35:55:294 [ info sync.configfile ]:    
Adding user defined ignore list to csync: 
"/home/fulbert/.config/ownCloud/sync-exclude.lst"
20210409_1235_owncloud.log.0.gz:04-09 12:35:55:295 [ warning gui.folder ]: 
Could not read system exclude file

After a little web search, I have not found a way to change the
path to the *system* `sync-exclude.lst` file, whether through GUI,
configuration file or environement variable.

brutal workaround :
$ mkdir $HOME/etc/ownCloud
$ ln -s $HOME/.guix-profile/etc/ownCloud/sync-exclude.lst $HOME/etc/ownCloud

Thanks and best regards.