Remove const from signal

We made a signal const. This does not make sense.

Task-number: QTBUG-94407
Pick-to: 6.2
Change-Id: I372da9c045ba880f8fba48399e441b53c1683e93
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>

src/corelib/animation/qsequentialanimationgroup.h

@@ -67,7 +67,7 @@ public:
     int duration() const override;
 
 Q_SIGNALS:
-    void currentAnimationChanged(QAbstractAnimation *current) const;
+    void currentAnimationChanged(QAbstractAnimation *current);
 
 protected:
     QSequentialAnimationGroup(QSequentialAnimationGroupPrivate &dd, QObject *parent);