Update debi.sh

debi.sh

@@ -717,7 +717,7 @@ EOF
 save_grub_cfg='cat'
 [ "$dry_run" = false ] && {
     base_url="$mirror_protocol://$mirror_host$mirror_directory/dists/$suite/main/installer-$architecture/current/images/netboot/debian-installer/$architecture"
-    [ "$suite" = stretch ] && [ "$efi" = true ] && base_url="$mirror_protocol://$mirror_host$mirror_directory/dists/bullseye/main/installer-$architecture/current/images/netboot/debian-installer/$architecture"
+    [ "$suite" = stretch ] && [ "$efi" = true ] && base_url="$mirror_protocol://$mirror_host$mirror_directory/dists/buster/main/installer-$architecture/current/images/netboot/debian-installer/$architecture"
     [ "$daily_d_i" = true ] && base_url="https://d-i.debian.org/daily-images/$architecture/daily/netboot/debian-installer/$architecture"
     firmware_url="https://cdimage.debian.org/cdimage/unofficial/non-free/firmware/$suite/current/firmware.cpio.gz"