Add local testing env variables
In order to get phpunit tests running locally, I had to run SIMPLETEST_DB=mysql://root:password@mariadb/db SIMPLETEST_BASE_URL=http://0.0.0.0:8888 vendor/bin/phpunit --bootstrap web/core/tests/bootstrap.php web/modules/custom
. We need to document this, or add these values into composer unit
script definition, or the plugin writes a phpunit.xml into the root dir, or something else.