B 7.0.x use light workflow

[joernott]

This PR switches the github actions to the univerasal light workflow.
There are a few things we should clarify fefore merging:

• I have noticed that phpcs was installed in composer.json but no tests/phpcs.xml was present. I've added that
• I also added configs for phpmd/phpstan and a 2nd test plan which also tests phpcs, phpmd and phpstan. We should discuss whether you want those tests to run and if you want them installed as part of require-dev in composer.json. Apart from phpstan reporting 81 errors which are "ignorable", they look OK. If you don't want those, I should remove the configs before merging