tst_QString::setRawData() indicates problems with Qt 6's reworking of raw data handling

During conversion of QString to use QArrayDataPointer, commit 287ace562ee5ddff22f7dbf4e49ae5f0520f2308, laknoll suppressed most of tst_QString::setRawData() with a

    QSKIP("This is currently not working.");

I've now converted that to three QEXPECT_FAIL(,,Continue) marking the parts that currently fail, but we need to follow up on this, either amending the test to match what's currently expected, or fixing the handling of raw data QString.