nixosTests.os-prober: fix filesystem for Debian

Debian's e2fsprogs does not understand the metadata_csum_seed ext4
feature, which our e2fsprogs enables by default, so we have to disable
it.

nixos/tests/os-prober.nix

@@ -8,7 +8,7 @@ let
       ${parted}/bin/parted --script /dev/vda mklabel msdos
       ${parted}/sbin/parted --script /dev/vda -- mkpart primary ext2 1M -1s
       mkdir /mnt
-      ${e2fsprogs}/bin/mkfs.ext4 /dev/vda1
+      ${e2fsprogs}/bin/mkfs.ext4 -O '^metadata_csum_seed' /dev/vda1
       ${util-linux}/bin/mount -t ext4 /dev/vda1 /mnt
 
       if test -e /mnt/.debug; then