meson: Find libcairo-script-interpreter when cairo is a subproject

If cairo is a subproject, it's not necessarily installed when gtk
is built. In the build tree, libcairo-script-interpreter is not stored
in the same directory as other cairo libraries.

gsk/meson.build

@@ -230,5 +230,5 @@ libgsk = static_library('gsk',
 # "public" libgtk_dep used by internal executables.
 libgsk_dep = declare_dependency(include_directories: [ confinc, ],
   sources: [ gskenum_h, ],
-  dependencies: libgdk_dep,
+  dependencies: [libgdk_dep, cairo_csi_dep],
 )