[LyX/2.3.x] Backport setTextColor deprecation fixes

[Juergen Spitzmueller]

commit 1a9bdb4452946f67a6eecbe119efd1d11f1563eb
Author: Juergen Spitzmueller <spitz at lyx.org>
Date:   Sat Mar 13 12:06:23 2021 +0100

    Backport setTextColor deprecation fixes
---
 src/frontends/qt4/PanelStack.cpp |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/src/frontends/qt4/PanelStack.cpp b/src/frontends/qt4/PanelStack.cpp
index e81d58c..414a098 100644
--- a/src/frontends/qt4/PanelStack.cpp
+++ b/src/frontends/qt4/PanelStack.cpp
@@ -212,7 +212,7 @@ static void setTreeItemStatus(QTreeWidgetItem * tree_item, bool enabled)
 	// Change the color from black to gray or viceversa
 	QPalette::ColorGroup new_color =
 		enabled ? QPalette::Active : QPalette::Disabled;
-	tree_item->setTextColor(0, QApplication::palette().color(new_color,
+	tree_item->setForeground(0, QApplication::palette().color(new_color,
 	                                                         QPalette::Text));
 }