x11/lavalauncher: unbreak build with librsvg >= 2.52

src/types/image_t.c:214:4: error: 'rsvg_handle_render_cairo' is deprecated: Use 'rsvg_handle_render_document' instead [-Werror,-Wdeprecated-declarations]

rsvg_handle_render_cairo(image->rsvg_handle, cairo);
^

/usr/local/include/librsvg-2.0/librsvg/rsvg-cairo.h:94:1: note: 'rsvg_handle_render_cairo' has been explicitly marked deprecated here
RSVG_DEPRECATED_FOR(rsvg_handle_render_document)
^
/usr/local/include/librsvg-2.0/librsvg/rsvg.h:50:32: note: expanded from macro 'RSVG_DEPRECATED_FOR'

^

/usr/local/include/glib-2.0/glib/gmacros.h:1112:44: note: expanded from macro 'G_DEPRECATED_FOR'

^

Reported by: antoine (via bug 258561 exp-run)