The function int32_t BSP_SD_Init(uint32_t Instance) (which I believe is the first thing to call to initialise access to the SD card on the STM32H747 Disco board) attempts to check if card detected on line 160. However the pin that is used as card detect isn't initialised until line 177, SD_MspInit(&hsd_sdmmc[Instance]). As it happens it doesn't really matter as the card is detected as present with the default setting for this pin (PI8) and the initialisation proceeds!
