const missing in class member declarations

[mverch67]

The two methods

String getValue(char *keys);
String getUnit(char *keys);

must be declared const char*:

String getValue(const char *keys);
String getUnit(const char *keys);

otherwise get compiler warnings when using this interface:

src/modules/Telemetry/Sensor/DFRobotLarkSensor.cpp: In member function 'virtual bool DFRobotLarkSensor::getMetrics(meshtastic_Telemetry*)':
src/modules/Telemetry/Sensor/DFRobotLarkSensor.cpp:38:80: warning: ISO C++ forbids converting a string constant to 'char*' [-Wwrite-strings]
     measurement->variant.environment_metrics.temperature = lark.getValue("Temp").toFloat();
                                                                                ^
src/modules/Telemetry/Sensor/DFRobotLarkSensor.cpp:39:86: warning: ISO C++ forbids converting a string constant to 'char*' [-Wwrite-strings]
     measurement->variant.environment_metrics.relative_humidity = lark.getValue("Humi").toFloat();
                                                                                      ^
src/modules/Telemetry/Sensor/DFRobotLarkSensor.cpp:40:80: warning: ISO C++ forbids converting a string constant to 'char*' [-Wwrite-strings]
     measurement->variant.environment_metrics.wind_speed = lark.getValue("Speed").toFloat();
                                                                                ^
src/modules/Telemetry/Sensor/DFRobotLarkSensor.cpp:41:109: warning: ISO C++ forbids converting a string constant to 'char*' [-Wwrite-strings]
     measurement->variant.environment_metrics.wind_direction = GeoCoord::bearingToDegrees(lark.getValue("Dir").c_str());
                                                                                                             ^
src/modules/Telemetry/Sensor/DFRobotLarkSensor.cpp:42:92: warning: ISO C++ forbids converting a string constant to 'char*' [-Wwrite-strings]
     measurement->variant.environment_metrics.barometric_pressure = lark.getValue("Pressure").toFloat();