fix(macros): 🐛 Fix for missing m600_idle_timeout variable

Adds the missing variable to smart_m600_dev

extras/filament_change/smart-m600_dev.cfg

@@ -50,6 +50,8 @@ variable_auto_unload: False             # Set this to True to have runouts and c
 variable_clean_nozzle: False            # Set this to True to perform a nozzle cleaning after loading
 variable_clean_macro: 'CLEAN_NOZZLE'    # Set this to the name of your nozzle cleaning macro
 
+variable_m600_idle_time: 3600           # Time to wait for user to change filament before resuming print
+
 # Do Not Change Below
 variable_coldstart: False
 variable_runout: False
@@ -134,7 +136,7 @@ gcode:
 ############ M600 ##############
 ################################
 [gcode_macro M600]
-gcode:
+gcode:''
     {% set m600cfg = printer["gcode_macro _m600cfg"] %}
     SET_IDLE_TIMEOUT TIMEOUT=7200 ; Increase idle timeout
     {% if printer.idle_timeout.state == "Printing" %}