[FIX] base: res.config.settings discard should actually discard changes

Before this commit, some values of res.config.settings were saved
(e.g case of website settings were some fields are related)

After this commit, they are not saved

OPW 1853230
closes #24972
closes #25028

odoo/addons/base/res/res_config_settings_views.xml

@@ -16,7 +16,7 @@
                         </div>
                         <header>
                             <button string="Save" type="object" name="execute" class="oe_highlight" />
-                            <button string="Discard" type="object" name="cancel" />
+                            <button string="Discard" type="object" name="cancel" special="cancel" />
                         </header>
                     </div>
                     <div class="o_setting_container">