Export also $PRETTY_DEBUG_EXCLUDE

It has no effect in subcommands otherwise.

src/app.skel

         "__SATURNIN_SHARE__/ini.d"
 )"
 
-export SATURNIN_CONF_PATH SHELLFU_PATH PRETTY_USAGE \
+export SATURNIN_CONF_PATH SHELLFU_PATH PRETTY_USAGE PRETTY_DEBUG_EXCLUDE \
        SATURNIN_CACHE_HOME SATURNIN_CONFIG_HOME SATURNIN_DATA_HOME
 
 saturnin__main "$@"