mkosi: Make sure systemd-libs is updated on Arch

The Arch Linux PKGBUILD does not (yet) have versioned dependencies
between the systemd packages, causing systemd-libs to not get updated
to 256-devel if systemd 256-devel is installed. Let's explicitly install
the newer version of systemd-libs as well for now until this problem is
fixed.

mkosi.images/system/mkosi.conf.d/10-arch/mkosi.conf

@@ -6,10 +6,11 @@ Distribution=arch
 [Content]
 VolatilePackages=
         systemd
-        systemd-ukify
-        systemd-sysvcompat
+        systemd-libs
         systemd-resolvconf
+        systemd-sysvcompat
         systemd-tests
+        systemd-ukify
 
 Packages=
         bpf
@@ -46,4 +47,5 @@ InitrdPackages=
 
 InitrdVolatilePackages=
         systemd
+        systemd-libs
         systemd-sysvcompat