Allow additional arguments to be passed to PHPUnit.

[longwave]

It is useful to be able to pass additional arguments to phpunit to run individual tests.

Before:

$ ddev xb-phpunit tests/src/Kernel/Plugin/Field/FieldType/ComponentTreeItemResolvedTest.php --filter testResolvedInvalidatedOnInputChange
PHPUnit 11.5.55 by Sebastian Bergmann and contributors.

Test file "modules/contrib/canvas/tests/src/Kernel/Plugin/Field/FieldType/ComponentTreeItemResolvedTest.php --filter testResolvedInvalidatedOnInputChange" not found

After:

$ ddev xb-phpunit tests/src/Kernel/Plugin/Field/FieldType/ComponentTreeItemResolvedTest.php --filter testResolvedInvalidatedOnInputChange
PHPUnit 11.5.55 by Sebastian Bergmann and contributors.

Runtime:       PHP 8.4.17
Configuration: /var/www/html/web/core/phpunit.xml.dist

F                                                                   1 / 1 (100%)

Time: 00:06.871, Memory: 25.30 MB

There was 1 failure:

1) Drupal\Tests\canvas\Kernel\Plugin\Field\FieldType\ComponentTreeItemResolvedTest::testResolvedInvalidatedOnInputChange
Failed asserting that two strings are identical.
--- Expected
+++ Actual
@@ @@
-'Updated heading'
+'Original heading'