borgmatic: only add postgres to closure if enabled

modules/nixos/services/borgmatic.nix

@@ -64,7 +64,8 @@ in
     ];
 
     # Add `pg_dumpall` to unit environment
-    systemd.services.borgmatic.path = [ config.services.postgresql.package ];
+    systemd.services.borgmatic.path =
+      if config.services.postgresql.enable then [ config.services.postgresql.package ] else [ ];
 
     # Without this override, `cat` is unavailable for `encryption_passcommand`
     systemd.services.borgmatic.confinement.fullUnit = true;