python - Setting non string variable using PyYaml

Question

I am using mkdocs system which is configured using yaml file, parsed via PyYml. I want to be able to specificy environment variable in its mkdocs.yml which is not possible in mkdocs ecosystem, but workaround exists using PyYml special !!python/object/apply:os.getenv syntax which works great for yaml keys of type string.

However, this doesn't work:

plugins:
    - search
    - pdf-export:
        combined: !!python/object/apply:os.getenv ["PDF_EXPORT_COMBINED"]

The build complains that string is not bool value:

PS> $Env:PDF_EXPORT_COMBINED='true'
PS> mkdocs build
...
ERROR - Config value: 'plugins'. Error: Plugin value: 'combined'. 
        Expected type: <class 'bool'> but received: <class 'str'>

I looked into PyYAML section YAML tags and Python types^1 to no avail. I guess form:

!python/object/apply:module.f | value of f(...)

could be used as I need pythons distutils.util.strtobool( os.getenv("PDF_EXPORT_COMBINED") ) but not sure if that is possible using that syntax.