fix: replace ComboBoxText.set_active_text() with model-based lookup

set_active_text() does not exist in GTK 3.24.x (only in GTK 4.x).
When loading a saved config with temperature_controller_type='simulated',
the set() method crashed on startup with AttributeError.

Added _set_combo_active_text() helper that iterates the model to find
the matching entry and calls set_active(index) instead.

src/damaris/gui/DamarisGUI.py

@@ -2396,7 +2396,7 @@ pygobject version %(pygobject)s
             try:
                 controller_type = config["temperature_controller_type"]
                 if controller_type in ["eurotherm", "simulated"]:
-                    self.config_temp_controller_type_combobox.set_active_text(controller_type)
+                    self._set_combo_active_text(self.config_temp_controller_type_combobox, controller_type)
                     # Update widget visibility based on type
                     self._update_temp_widgets_visibility()
             except (TypeError, ValueError):
@@ -2410,7 +2410,7 @@ pygobject version %(pygobject)s
             try:
                 baudrate = str(config["temperature_baudrate"])
                 if baudrate in ["9600", "19200", "38400", "57600", "115200"]:
-                    self.config_temp_baudrate_combobox.set_active_text(baudrate)
+                    self._set_combo_active_text(self.config_temp_baudrate_combobox, baudrate)
                 else:
                     self.config_temp_baudrate_combobox.set_active(0)  # Default to 19200
             except (TypeError, ValueError):
@@ -2496,6 +2496,24 @@ pygobject version %(pygobject)s
             else:
                 self.config_temp_baudrate_hbox.hide()
 
+    def _set_combo_active_text(self, combobox, text):
+        """
+        Set a ComboBoxText's active entry by text.
+        
+        Gtk.ComboBoxText.set_active_text() does not exist in GTK 3.24.x,
+        so we iterate the model to find the matching entry.
+        """
+        if not text:
+            return
+        model = combobox.get_model()
+        if model is None:
+            return
+        for i in range(model.iter_n_children(None)):
+            iter = model.iter_nth_child(None, i)
+            if iter and model.get(iter, 0)[0] == text:
+                combobox.set_active(i)
+                return
+
     def load_config_handler( self, widget ):
         if self.system_default_filename:
             self.load_config( self.system_default_filename )