Update M49.cpp

Marlin/src/gcode/bedlevel/ubl/M49.cpp

 void GcodeSuite::M49() {
   g26_debug_flag ^= true;
   SERIAL_PROTOCOLPGM("G26 Debug: ");
-  serialprintPGM(g26_debug_flag ? PSTR("On") : PSTR("Off"));
-  SERIAL_EOL();
+  serialprintPGM(g26_debug_flag ? PSTR("On\n") : PSTR("Off\n"));
 }
 
 #endif // G26_MESH_VALIDATION