Don't depend on python 3.6 when the python option is deselected.
However syslog-ng* does depend on glib20. glib20 does depend on
python and if python is deslected the default python27 is installed
by glib20. If OTOH the python option is selected, python36 is installed
and glib20 will use it instead. Installing syslog-ng without python
support and subsequently changing one's mind to later depend on
python will result in both python27 and python36 to be installed.

PR: 236845
Inspired by: leres@