QTest: Make QCOMPARE of QCborError produce output

I was getting:
   Actual   (reader.validate())  : <null>
   Expected (QCborError::NoError): NoError

Change-Id: Ib47c56818178458a88b4fffd1554f1751f447086
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

src/testlib/qtest.h

@@ -49,6 +49,7 @@
 #include <QtCore/qbytearray.h>
 #include <QtCore/qstring.h>
 #include <QtCore/qstringlist.h>
+#include <QtCore/qcborcommon.h>
 #include <QtCore/qdatetime.h>
 #include <QtCore/qobject.h>
 #include <QtCore/qvariant.h>
@@ -110,6 +111,12 @@ template<> inline char *toString(const QDateTime &dateTime)
 }
 #endif // datestring
 
+template<> inline char *toString(const QCborError &c)
+{
+    // use the Q_ENUM formatting
+    return toString(c.c);
+}
+
 template<> inline char *toString(const QChar &c)
 {
     const ushort uc = c.unicode();