Describe the bug

Basically, there needs to be a slight amendment to #10079

cc @pradyunsg

How to Reproduce

I come across this when running tests with sphinx fixtures

pytest_plugins = 'sphinx.testing.fixtures'

@pytest.mark.sphinx('html', confoverrides={'pygments_dark_style': 'other'})
def test_html4_output(app, status, warning):
   # but pygments_dark_style wil not be set
    app.build()

Expected behavior

No response

Your project

furo

Screenshots

No response

OS

any

Python version

any

Sphinx version

4.3.2

Sphinx extensions

No response

Extra tools

No response

Additional context

No response