video/meson.build: declare dependency on cairo as well
This is followup for 062a4c27
While we do check for a cairo-png dependency, the png API is part of cairo.h header with a feature toggle. So we need cairo depencency as well.
../subprojects/gst-devtools/validate/gst-libs/gst/video/gstvalidatessim.c(31):
fatal error C1083: Cannot open include file: 'cairo.h': No such file or
directory