add needed type hints for phpunit8

This will break a lot of plugin tests, but can't be avoided

mark some tests as non-risky

Those tests either just check that an exception is NOT thrown or are
there to check dependencies for other tests. Newer phpunits mark all
tests as risky that have no ass

mark some tests as non-risky

Those tests either just check that an exception is NOT thrown or are
there to check dependencies for other tests. Newer phpunits mark all
tests as risky that have no assertion.

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changed tests to use a data provider

this allows for each dump being run within its own test case which then
can be skipped. This is needed to skip the django test on older PHP
versions.

added a postgres example database to the tests

added fluxbb dump to the tests.

now all capabilities are covered

added a few more tests for wordpress

first go at using real database dumps for tests

this configures a minimal wordpress setup