Tweak probe debug, add newline

Marlin/Marlin_main.cpp

 
       #if ENABLED(DEBUG_LEVELING_FEATURE)
         float first_probe_z = current_position[Z_AXIS];
-        if (DEBUGGING(LEVELING))
-          SERIAL_ECHOPAIR("1st Probe Z:", first_probe_z);
+        if (DEBUGGING(LEVELING)) SERIAL_ECHOLNPAIR("1st Probe Z:", first_probe_z);
       #endif
 
       // move up by the bump distance