TerminalPane: Fix a warning about an unused arg

Change-Id: I63d19a608c63532e0e83df929da6cb07dc896722
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/terminal/terminalpane.cpp

@@ -163,6 +163,7 @@ TerminalWidget *TerminalPane::stoppedTerminalWithId(Id identifier) const
 
 QWidget *TerminalPane::outputWidget(QWidget *parent)
 {
+    Q_UNUSED(parent)
     if (!m_widgetInitialized) {
         m_widgetInitialized = true;
         m_tabWidget.setTabBarAutoHide(false);