Qt5 CI: run `make check' for qtqa

qtqa should be running `make check' for itself. This is a bit of a special case as we actually want `make check' for qtqa to run the perl autotests (e.g. `prove -r'). It's unclear exactly how the "shared" tests in qtqa should be handled.

It is fairly high priority, since we now host the test scripts in qtqa. Otherwise anyone can easily check in something to qtqa which (for example) silently makes all test scripts exit with 0 exit code and therefore makes all tests pass, causing massive damage...