Replace 'boolean' with 'bool'

[ademuri]

This fixes warnings on STM32 about boolean being deprecated:

In file included from .pio/libdeps/default/Adafruit ST7735 and ST7789 Library/Adafruit_ST7789.h:4,                                   
                 from /home/adam/hardware/gps-tracker/src/gps-tracker.ino:4:                                                         
.pio/libdeps/default/Adafruit ST7735 and ST7789 Library/Adafruit_ST77xx.h:102:36: warning: 'boolean' is deprecated [-Wdeprecated-declarations]
  102 |   void enableDisplay(boolean enable);                                                                                        
      |                                    ^                                                                                         
In file included from /home/adam/.platformio/packages/framework-arduinoststm32/cores/arduino/wiring.h:34,                            
                 from /home/adam/.platformio/packages/framework-arduinoststm32/cores/arduino/Arduino.h:36,                           
                 from /tmp/tmpiqlma7tp:1:                                                                                            
/home/adam/.platformio/packages/framework-arduinoststm32/cores/arduino/wiring_constants.h:110:14: note: declared here                
  110 | typedef bool boolean __attribute__((deprecated));                                                                            
      |              ^~~~~~~