QProxyStyle doesn't support nested QProxyStyles

A temporary solution is to not initialize the collapsible groupbox style
with the current style.
See Issue #24279
https://bugreports.qt-project.org/browse/QTBUG-24279

Libs/Widgets/ctkCollapsibleGroupBox.cpp

@@ -117,7 +117,7 @@ void ctkCollapsibleGroupBoxPrivate::init()
 
   this->MaxHeight = q->maximumHeight();
 #if QT_VERSION >= 0x040600
-  q->setStyle(new ctkCollapsibleGroupBoxStyle(q->style()));
+  q->setStyle(new ctkCollapsibleGroupBoxStyle(0));
 #else
   this->setStyleSheet(
     "ctkCollapsibleGroupBox::indicator:checked{"