Tooltips: Fix unassigned strip_edges() call on text

Fixes #43940, was a regression from #43280.

(cherry picked from commit a4af94068a6223b4d0a5f5f8d7921742812bcfb9)

scene/main/viewport.cpp

@@ -1590,7 +1590,7 @@ void Viewport::_gui_show_tooltip() {
 			gui.tooltip_control,
 			gui.tooltip_control->get_global_transform().xform_inv(gui.tooltip_pos),
 			&tooltip_owner);
-	tooltip_text.strip_edges();
+	tooltip_text = tooltip_text.strip_edges();
 	if (tooltip_text.empty()) {
 		return; // Nothing to show.
 	}