How to load a YAML 1.1 file without the YAML directive?

Question

Using ruamel.yaml v0.17.20, I'm trying to load files produced with PyYAML (or written by authors for software that only uses PyYAML). These files do not have a YAML directive, but PyYAML only supports YAML 1.1, so I need to somehow inform ruamel.yaml that it should load the file with 1.1, even though there isn't a directive.

from pathlib import Path
from ruamel.yaml import YAML

yaml = YAML()
yaml.version = (1, 1)
yaml.load(Path("some/path/to/file.yml"))  # file.yml exists and does not have a YAML directive

print(yaml.version)  # prints None
assert yaml.version == (1, 1)  # this fails!

When I try to load a file without a YAML directive, the Parser overwrites my explicitly set yaml.version with None in Parser.process_directives():

    def process_directives(self):
        # ...
        yaml_version = None
        # code that loads directives (but there aren't any in my case)

        if self.loader is not None and hasattr(self.loader, 'tags'):
            self.loader.version = yaml_version
            # ...

https://sourceforge.net/p/ruamel-yaml/code/ci/default/tree/parser.py#l316

The load version matters for things like parsing octals and booleans.

How can I tell ruamel.yaml to use 1.1 when parsing a stream that is missing a YAML directive?