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Description
This is mostly useful for the failOn* settings, but it might apply to other boolean settings.
Currently, the CLI flag can turn those settings on if the config file does not, but it cannot turns them off.
We have a use case in the Symfony CI where we want to fail on deprecations by default (including for contributors running it locally) but we have a specific CI job (the one installing the dependencies with --prefer-lowest) where we want to disable it.
Being able to run phpunit --no-fail-on-deprecations to turn off the setting would be perfect, as it means we could turn it on in the config file (making the experience better for contributors running it locally as they would have the expected failures by default)