tst_HandshakeRequest::tst_qtbug_48123(headerline too long) Compared values are not the same

The dependency update for qtwebsockets in the 6.4 branch fails (this is blocking the dependency update round in 6.4 so added a P0 priority):

https://codereview.qt-project.org/c/qt/qtwebsockets/+/419561

7804: ********* Start testing of tst_HandshakeRequest *********
 FAIL!  : tst_HandshakeRequest::tst_qtbug_48123(headerline too long) Compared values are not the same
    Actual   (request.isValid()): 1
    Expected (shouldBeValid)    : 0
    Loc: [/Users/qt/work/qt/qtwebsockets/tests/auto/websockets/handshakerequest/tst_handshakerequest.cpp(384)]
 Totals: 2 passed, 1 failed, 0 skipped, 0 blacklisted, 1ms

Build log:

https://testresults.qt.io/logs/qt/qtwebsockets/0ef9e1cdd8ed8cc188a0c60fe8e54a6eb4395c8d/MacOSMacOS_11_00arm64MacOSMacOS_11_00arm64Clangqtci-macos-11.0-arm64TestOnly/a0b5dd0e16b1aaef213e1b294eddba6b881a2822/test_1656569817/log.txt.gz

Details: https://testresults.qt.io/coin/integration/qt/qtwebsockets/tasks/1656569771

Please note a comment from Mårten Nordheim (linked patch done to dev, not yet merged):
Something's wrong in websockets, not sure what. I broke some of it, patch here: https://codereview.qt-project.org/c/qt/qtwebsockets/+/419915
I'm not sure what causes tst_HandshakeRequest::tst_qtbug_57357 to fail though