Clangd: Fix autocompletion for old style SIGNAL and SLOT

Fixes: QTCREATORBUG-20737
Change-Id: If6d3c6ea5924537386eca81d90d4bb1e8f1a1466
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/qmljseditor/qmljsquickfixassist.h

@@ -45,6 +45,7 @@ public:
 
     const QmlJSTools::SemanticInfo &semanticInfo() const;
     QmlJSTools::QmlJSRefactoringFilePtr currentFile() const;
+    bool isBaseObject() const override { return false; }
 
 private:
     QmlJSTools::SemanticInfo m_semanticInfo;