Add a test for SAVED_POSITIONS

buildroot/tests/mega2560

 # Test a probeless build of AUTO_BED_LEVELING_UBL, with lots of extruders
 #
 use_example_configs AnimationExample
-opt_set MOTHERBOARD BOARD_AZTEEG_X3_PRO LCD_LANGUAGE fr \
+opt_set MOTHERBOARD BOARD_AZTEEG_X3_PRO LCD_LANGUAGE fr SAVED_POSITIONS 4 \
         EXTRUDERS 5 TEMP_SENSOR_1 1 TEMP_SENSOR_2 5 TEMP_SENSOR_3 20 TEMP_SENSOR_4 1000 TEMP_SENSOR_BED 1
 opt_enable AUTO_BED_LEVELING_UBL RESTORE_LEVELING_AFTER_G28 DEBUG_LEVELING_FEATURE G26_MESH_VALIDATION ENABLE_LEVELING_FADE_HEIGHT SKEW_CORRECTION \
            REPRAP_DISCOUNT_FULL_GRAPHIC_SMART_CONTROLLER LIGHTWEIGHT_UI STATUS_MESSAGE_SCROLLING SHOW_CUSTOM_BOOTSCREEN BOOT_MARLIN_LOGO_SMALL \