[FIX] point_of_sale: close session from pos config

There was a traceback when closing the session from the pos config.
Step to reproduce:
 1. Open a session
 2. Go to the pos config
 3. Try to close the session

 This commit allows the user to close the session from the config.

closes odoo/odoo#102581

X-original-commit: a34c9ab209c7859ed500fb44d580cc546e56bd37
Signed-off-by: Trinh Jacky (trj) <trj@odoo.com>

addons/point_of_sale/models/res_config_settings.py

@@ -173,7 +173,7 @@ class ResConfigSettings(models.TransientModel):
 
     def pos_open_ui(self):
         if self._context.get('pos_config_id'):
-            pos_config_id = self._context['pos_config_id'][0]
+            pos_config_id = self._context['pos_config_id']
             pos_config = self.env['pos.config'].browse(pos_config_id)
             return pos_config.open_ui()