Update test/test_slcan.py

Type fix in slcan test

Co-authored-by: zariiii9003 <[email protected]>

Author: BroderickJack

test/test_slcan.py

@@ -39,7 +39,7 @@ def test_recv_extended(self):
         self.assertSequenceEqual(msg.data, [0xAA, 0x55])
 
         # Ewert Energy Systems CANDapter specific
-        elf.serial.write(b"x12ABCDEF2AA55\r")
+        self.serial.write(b"x12ABCDEF2AA55\r")
         msg = self.bus.recv(TIMEOUT)
         self.assertIsNotNone(msg)
         self.assertEqual(msg.arbitration_id, 0x12ABCDEF)