It shows up here:
(but that's the "live" trunk, not the most recently released library.)
From my previous test sketch, that probably means you can change it like so:
#elif defined(ARDUINO_UNOR4_MINIMA) || defined(ARDUINO_NANO_R4)
//0, 1, 2, 3, 8, 12, 13, 15, 16, 17, 18 and 19.
#define CORE_NUM_INTERRUPT 20
#define CORE_INT0_PIN 0
#define CORE_INT1_PIN 1
#define CORE_INT2_PIN 2
#define CORE_INT3_PIN 3
#define CORE_INT8_PIN 8
#define CORE_INT12_PIN 12
#define CORE_INT13_PIN 13
#define CORE_INT15_PIN 15
#define CORE_INT16_PIN 16
#define CORE_INT17_PIN 17
#define CORE_INT18_PIN 18
#define CORE_INT19_PIN 19