make it OK to call auto_dim_display if brightness is not settable

Author: jepler

adafruit_pybadger/pybadger_base.py

@@ -421,6 +421,8 @@ def auto_dim_display(self, delay: float = 5.0, movement_threshold: int = 10):
             while True:
                 pybadger.auto_dim_display(delay=10)
         """
+        if not hasattr(self.display, "brightness"):
+            return
         current_time = time.monotonic()
         if self._check_for_movement(movement_threshold=movement_threshold):
             self.activity(current_time)