Test fail on MacOS because of gnused feature

When running behat tests on macOS I saw this failure:

--- Failed steps:

001 Scenario: BOM found in wp-config.php file                                 # features/config.feature:548
      And I run `sed -i '1s/^\(\xef\xbb\xbf\)\?/\xef\xbb\xbf/' wp-config.php` # features/config.feature:566
        $ sed -i '1s/^\(\xef\xbb\xbf\)\?/\xef\xbb\xbf/' wp-config.php

        sed: -I or -i may not be used with stdin
        cwd: /var/folders/nc/16hfjyf9517918dd0dz2g7tr0000gn/T/wp-cli-test-run--63bd7a0a590628.51883440/
        run time: 0.017526865005493
        exit status: 1 (RuntimeException)

Which comes from

And I run `sed -i '1s/^\(\xef\xbb\xbf\)\?/\xef\xbb\xbf/' wp-config.php`

Some scripts try to get around this with a check like: https://github.com/wp-cli/sample-plugin/blob/master/bin/install-wp-tests.sh#L96-L101 though I'm not sure what is supported in these .feature files