QCborStreamReader: fix API mistake: lastError() wasn't const

[ChangeLog][QtCore][QCborStreamReader] Fixed lastError() not being
declared as a const member.

Change-Id: Ib1d2fc7100134f7597cdfffd174a8401b43576d4
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

src/corelib/compat/removed_api.cpp

@@ -672,6 +672,13 @@ QByteArray QByteArray::chopped(qsizetype n) const
 { return sliced(0, size() - n); }
 #endif
 
+#include "qcborstreamreader.h"
+
+QCborError QCborStreamReader::lastError()
+{
+    return std::as_const(*this).lastError();
+}
+
 #include "qdatetime.h"
 
 QDateTime::QDateTime(QDate date, QTime time, const QTimeZone &timeZone)

src/corelib/serialization/qcborstreamreader.cpp

@@ -929,7 +929,7 @@ void QCborStreamReader::reset()
 
    \sa isValid()
  */
-QCborError QCborStreamReader::lastError()
+QCborError QCborStreamReader::lastError() const
 {
     return d->lastError;
 }

src/corelib/serialization/qcborstreamreader.h

@@ -77,7 +77,10 @@ public:
     void clear();
     void reset();
 
+#if QT_CORE_REMOVED_SINCE(6, 6)
     QCborError lastError();
+#endif
+    QCborError lastError() const;
 
     qint64 currentOffset() const;