composefs/boot: Fix sd-boot order on update

Grub sorts its BLS config in descending order, while sd-boot sorts the
configs in ascending order. While upgrading we were always setting the
new sort key to be `1` which would work for Grub but not for sd-boot.

Fixes: #1777

Signed-off-by: Pragyan Poudyal <pragyanpoudyal41999@gmail.com>

Author: Johan-Liebert1

crates/lib/src/bootc_composefs/boot.rs

@@ -474,7 +474,11 @@ pub(crate) fn setup_composefs_bls_boot(
             let boot_digest = compute_boot_digest(usr_lib_modules_vmlinuz, &repo)
                 .context("Computing boot digest")?;
 
-            let default_sort_key = "1";
+            let default_sort_key = match bootloader {
+                Bootloader::Grub => "1",
+                Bootloader::Systemd => "0",
+            };
+
             let default_title_version = (id.to_hex(), default_sort_key.to_string());
 
             let osrel_res = osrel_title_and_version(fs, &repo)?;
@@ -540,7 +544,11 @@ pub(crate) fn setup_composefs_bls_boot(
         let boot_dir = Dir::open_ambient_dir(&entry_paths.config_path, ambient_authority())?;
 
         let mut booted_bls = get_booted_bls(&boot_dir)?;
-        booted_bls.sort_key = Some("0".into()); // entries are sorted by their filename in reverse order
+        booted_bls.sort_key = match bootloader {
+            // Grub entries are sorted by their filename in reverse order
+            Bootloader::Grub => Some("0".into()),
+            Bootloader::Systemd => Some("1".into()),
+        };
 
         // This will be atomically renamed to 'loader/entries' on shutdown/reboot
         (