Secure Boot: update grub and shim binaries

Update to shim-signed + grub-efi-amd64-signed as present in current
Debian/unstable + testing AKA trixie.

Thanks: pasja
Closes: #168

templates/EFI/debian/BOOT/README

@@ -1,6 +1,6 @@
 # debian approach:
-shimx64.efi.signed = /usr/lib/shim/shimx64.efi.signed                  from https://deb.debian.org/debian/pool/main/s/shim-signed/shim-signed_1.38+15.4-7_amd64.deb
-grubx64.efi.signed = /usr/lib/grub/x86_64-efi-signed/gcdx64.efi.signed from https://deb.debian.org/debian/pool/main/g/grub-efi-amd64-signed/grub-efi-amd64-signed_1+2.06+7_amd64.deb
+shimx64.efi.signed = /usr/lib/shim/shimx64.efi.signed                  from https://deb.debian.org/debian/pool/main/s/shim-signed/shim-signed_1.44+15.8-1_amd64.deb
+grubx64.efi.signed = /usr/lib/grub/x86_64-efi-signed/gcdx64.efi.signed from https://deb.debian.org/debian/pool/main/g/grub-efi-amd64-signed/grub-efi-amd64-signed_1+2.12+5_amd64.deb
 # NOTE:
 # shimx64.efi.signed ends up as /EFI/BOOT/bootx64.efi inside [grml_cd]/boot/efi.img, and
 # grubx64.efi.signed ends up as /EFI/BOOT/grubx64.efi inside [grml_cd]/boot/efi.img, whereas