Fix type of Tap Dance max index variable (#14887)

quantum/process_keycode/process_tap_dance.c

@@ -20,7 +20,7 @@ uint8_t get_oneshot_mods(void);
 #endif
 
 static uint16_t last_td;
-static int8_t   highest_td = -1;
+static int16_t  highest_td = -1;
 
 void qk_tap_dance_pair_on_each_tap(qk_tap_dance_state_t *state, void *user_data) {
     qk_tap_dance_pair_t *pair = (qk_tap_dance_pair_t *)user_data;