community/inkscape: update $depends for working SVG export

Without py3-lxml, py3-cssselect, and py3-numpy the SVG export feature of Inkscape doesn't work. Strictly speaking, one could argue that these are optional dependencies as it seems that they are not required if no SVGs are exported. However, I would argue that SVG exporting is a central feature of an SVG editor like inkscape and would therefore like to see these libraries be added to $depends. Furthermore, other Linux distributions (e.g. Arch Linux) also track the aforementioned libraries as mandatory run-time dependencies.