Fix Behat code coverage report

[swissspidy]

IIRC code coverage for the Behat tests never properly worked with pcov.

I just got it working at WordPress/plugin-check#215 with xdebug though. So would be nice to do that here as well.

Another main issue with the setup here is that the source folders are configured incorrectly:

traduttore/tests/behat/maybe-generate-wp-cli-coverage.php

Lines 15 to 16 in a9faec1

	$filter->includeDirectory( "{$root_folder}/includes" );
	$filter->includeDirectory( "{$root_folder}/src" );

It should be inc.

Also, including the traduttore.php file would make sense.