PyYAML implements YAML spec version 1.1, not 1.2. Hence, values starting
with `0o` are not considered as numbers: they are just strings, so they
need quotes when `quoted-strings: {required: true}`.
>>> import yaml
>>> yaml.resolver.Resolver().resolve(yaml.nodes.ScalarNode, '100', (True, False))
'tag:yaml.org,2002:int'
>>> yaml.resolver.Resolver().resolve(yaml.nodes.ScalarNode, '0100', (True, False))
'tag:yaml.org,2002:int'
>>> yaml.resolver.Resolver().resolve(yaml.nodes.ScalarNode, '0o100', (True, False))
'tag:yaml.org,2002:str'
Let's try to prevent that.
Fixes https://github.com/adrienverge/yamllint/issues/351.
1b378ed5b9