Tests: Revert the `dirname( __FILE__ )` replacement in...

Tests: Revert the `dirname( __FILE__ )` replacement in `wp-tests-config-sample.php` for now, to avoid breaking unit tests created with WP-CLI `scaffold` command.

Follow-up to [47198].

Props kaggdesign, danielbachhuber, bwmarkle.
Fixes #48082, #49377.
Built from https://develop.svn.wordpress.org/trunk@47201


git-svn-id: https://core.svn.wordpress.org/trunk@47001 1a063a9b-81f0-0310-95a4-ce76da25c4cd