[fix] Work around ynh bug random string too big

scripts/install

@@ -23,7 +23,7 @@ zoom=$YNH_APP_ARG_ZOOM
 cnil_link=$YNH_APP_ARG_CNIL_LINK
 cnil_number=$YNH_APP_ARG_CNIL_NUMBER
 url_contact=$YNH_APP_ARG_URL_CONTACT
-secret=$(ynh_string_random 120)
+secret=$(ynh_string_random 24) # A bug don't allow to do random string bigger than 24
 
 
 # Check if admin exists