PhpUnit: added & update some tests

[sreichel]

• [x] merged phpunit and sonar, to not run tests twice
• [x] added tests to php-cs-fixer/phpcs checks
• [x] added tests to phpstan (passing Level 9)
• [x] updated some tests and added test from testfield
• [x] install Openmage database for tests

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Test: run vendor/bin/phpunit

• closes https://github.com/OpenMage/magento-lts/issues/4139

Todo: (another PR)

Publish sonar results for UnitTests.

[sreichel]

For local tests in phpstorm ...

• run phpunit with coverage (see ddev command)
• in phpstorm hit alt+ctrl+6 to select coverage file
• select clover.xml from dev/tests directory

You should see which files/lines are covered by tests.