Ignore libovla doctests

This is an "external" library that contains non-passing doctest-like
docs.

Signed-off-by: Philippe Ombredanne <pombredanne@nexb.com>

Author: pombredanne

setup.cfg

@@ -54,4 +54,5 @@ addopts =
     -rfEsxXw
     --strict
     --ignore setup.py
+    --ignore vulnerabilities/lib_oval.py
     --doctest-modules