extend-immutable-calls: how to configure?

I haven’t been able to make the recently released feature extend-immutable-calls to work.

Have I configured it wrong?

I have verified that flake8 recognizes the config, by setting the line-length to 10 and verified flake8 warnings about line length.

flake8 --version

4.0.1 (flake8-bugbear: 21.11.29, mccabe: 0.6.1, pycodestyle: 2.8.0, pyflakes: 2.4.0) CPython 3.10.0 on
Darwin

example.py

import fastapi


def example_fn(data: str = fastapi.Header(None)):
    pass

setup.cfg

[flake8]
max-line-length = 120
extend-immutable-calls = ["fastapi.Header"]

flake8 --show-source

./example.py:4:28: B008 Do not perform function calls in argument defaults.  The call is performed only once at function definition time. All calls to your function will reuse the result of that definition-time function call.  If this is intended, assign the function call to a module-level variable and use that variable as a default value.
def example_fn(data: str = fastapi.Header(None)):
                           ^

[sco1]

You want:

[flake8]
max-line-length = 120
extend-immutable-calls = fastapi.Header

[aberres]

Same problem here - I tried to silence pathlib.Path.