This PR makes it less strict to check for the existence of a tests folder in the main directory of the project. It can be useful for projects that prefer to test in some other weird folder. For example.

# A structure of a scripting project only

├── app
│   │── fibonacci.php
│   └── fibonacci_test.php
├── composer.json
├── composer.lock
└── phpunit.xml

<!-- phpunit.xml -->

<testsuite name="Test Suite">
    <directory suffix="_test.php">./app</directory>
</testsuite>

Note that my tests are simple files with a suffix _test.php in a folder other than tests, so with the current version of pest, if I run vendor/bin/pest it will fail with an exception of type InvalidUsesPath.

Also contributing to #283