raylib: fix temporarily untoggleable onroad experimental mode button (#36383)

* gpt got it after 2 tries, but still not immed mergeable

* bad bot

selfdrive/ui/onroad/exp_button.py

@@ -66,8 +66,5 @@ class ExpButton(Widget):
     if not self._params.get_bool("ExperimentalModeConfirmed"):
       return False
 
-    car_params = ui_state.sm["carParams"]
+    # Mirror exp mode toggle using persistent car params
-    if car_params.alphaLongitudinalAvailable:
+    return ui_state.has_longitudinal_control
-      return self._params.get_bool("AlphaLongitudinalEnabled")
-    else:
-      return car_params.openpilotLongitudinalControl