images.fc: fix opening with kernel 5.15

We're still using kernel 5.15 in our VMs for now. Opening the XFS from
the VM image had failed due to incompatible XFS features.

`nrext64` is only availabe from 5.19 on and non-experimental since 6.5,
so we need to explicitly disable that feature for now when writing
images.

release/make-disk-image.nix

@@ -113,12 +113,13 @@ let format' = format; in let
       # mkfs.xfs does not support --offset, so we must place a separately
       # generated XFS image into the main disk image.
       truncate -s ''${sizeMB}M rootfs.img
-      mkfs.xfs -L ${rootLabel} rootfs.img
+      # TODO: nrext64 can be enabled again once we are at kernel >= 6.5 in the VMs
+      mkfs.xfs -i nrext64=0 -L ${rootLabel} rootfs.img
       dd if=rootfs.img of=$diskImage bs=1M seek=$startMB count=$sizeMB \
         conv=sparse,notrunc iflag=direct
       rm rootfs.img
     '' else ''
-      mkfs.xfs -L ${rootLabel} $diskImage
+      mkfs.xfs -i nrext64=0 -L ${rootLabel} $diskImage
     ''}
 
     root="$PWD/root"