zfsUnstable -> zfs_unstable

nixpkgs has a new path for this.

nixosModules/bcachefs.nix

@@ -5,7 +5,7 @@
 }:
 {
   # If we also need zfs, we can use the unstable version as we otherwise don't have a new enough kernel version
-  boot.zfs.package = pkgs.zfsUnstable;
+  boot.zfs.package = pkgs.zfs_unstable or pkgs.zfsUnstable;
 
   # Enable bcachefs support
   boot.supportedFilesystems.bcachefs = lib.mkDefault true;

nixosModules/installer/zfs-latest.nix

@@ -6,7 +6,7 @@
 }:
 
 let
-  isUnstable = config.boot.zfs.package == pkgs.zfsUnstable;
+  isUnstable = config.boot.zfs.package == pkgs.zfs_unstable or pkgs.zfsUnstable;
   zfsCompatibleKernelPackages = lib.filterAttrs (
     name: kernelPackages:
     (builtins.match "linux_[0-9]+_[0-9]+" name) != null