[python-xhtml2pdf-pip][TEMP] add libcairo2-dev (#369)

pygobject/pycairo#319

Author: MatthijsBurgh

python-xhtml2pdf-pip/install.yaml

@@ -1,2 +1,7 @@
+# [TEMP] Needed because of reportlab-4.0, dep of xhtml2pdf.
+# See https://github.com/pygobject/pycairo/issues/319 to see when to delete
+- type: system
+  name: libcairo2-dev
+
 - type: pip
   name: xhtml2pdf