Fix Keysight test

Signed-off-by: Travis F. Collins <[email protected]>

tests/test_keysight.py

@@ -4,7 +4,7 @@
 def test_e36233a_auto():
     ps = keysight.E36233A()
     # Read all properties from all channels
-    for chan in ps.channels:
+    for chan in ps.channels():
         print(f"Channel {chan.channel_number}:")
         print(f"Voltage: {chan.voltage}")
         print(f"Current: {chan.current}")