build: bump libyaml

Patch updates libyaml to the version that contains fixes of stack
overflows [1]. PR in upstream with original patch: "Avoid recursion in
the document loader" [2].

1. https://github.com/yaml/libyaml/issues/107
2. https://github.com/yaml/libyaml/pull/127

NO_DOC=internal
NO_TEST=internal