QSignalSpy: fix clazy-function-args-by-value

Clazy complains that QMetaMethod should be passed by value, so do
that.

Change-Id: I42afda5af6910eefc8783b1feac00fd11e1f017e
Reviewed-by: David Faure <david.faure@kdab.com>

src/testlib/qsignalspy.h

@@ -80,7 +80,7 @@ public:
     }
 #endif // Q_QDOC
 
-    QSignalSpy(const QObject *obj, const QMetaMethod &signal)
+    QSignalSpy(const QObject *obj, QMetaMethod signal)
     {
         if (isObjectValid(obj) && isSignalMetaMethodValid(signal)) {
             initArgs(signal, obj);

src/testlib/qsignalspy.qdoc

@@ -74,7 +74,7 @@
     \snippet code/doc_src_qsignalspy.cpp 6
 */
 
-/*! \fn QSignalSpy::QSignalSpy(const QObject *obj, const QMetaMethod &signal)
+/*! \fn QSignalSpy::QSignalSpy(const QObject *obj, QMetaMethod signal)
     \since 5.14
 
     Constructs a new QSignalSpy that listens for emissions of the \a signal