Migrate PHPUnit configuration

[gdejong]

While running some tests I noticed this warning:

PHPUnit 9.4.3 by Sebastian Bergmann and contributors.

Runtime:       PHP 7.4.12 with Xdebug 2.9.8
Configuration: /opt/project/phpunit.xml.dist
Random Seed:   1606407050
Warning:       Your XML configuration validates against a deprecated schema.
Suggestion:    Migrate your XML configuration using "--migrate-configuration"!

As suggested, I used vendor/bin/phpunit --migrate-configuration to perform the migration, followed by some manual reformatting.

The migration refactored xsi:noNamespaceSchemaLocation to point to https://schema.phpunit.de/9.3/phpunit.xsd. I reverted that to ./vendor/phpunit/phpunit/phpunit.xsd but if you want I can change it to point to schema.phpunit.de

[gdejong]

See https://twitter.com/s_bergmann/status/1269917026107248641 / https://github.com/sebastianbergmann/phpunit/blob/9.3.11/ChangeLog-9.3.md

[muglug]

Thanks!