qt6: use auto & in the lambda in the jsonhelper.h
qt6: use auto & in the lambda in the jsonhelper.h

In qt6, QJsonArrayRef cannot be implicitly converted to QVariant, but we
don't need that, we can simply call .toString() on the QJsonArrayRef
object.

Change-Id: I8cf394133f12946b195211df217e9d42c8d14fa5
Reviewed-by: Christian Kandeler <3aa99dcdd3f0cac61fb81c2a11771c0cc2497607@qt.io>

qt-labs/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,qt-labs/qbs,qt-labs/qbs,qtproject/qt-labs-qbs