nixos/immich: fix postgresql.package regression

`config.services.postgresql.package` is now only available when the
PostgreSQL module is actually enabled. If we're not using the local
database, we'll need to fallback to the latest postgresql version, since
we don't know about the remote version.

(cherry picked from commit 62d2b6d593)

nixos/modules/services/web-apps/immich.nix

@@ -46,6 +46,9 @@ let
     mkOption
     mkEnableOption
     ;
+
+  postgresqlPackage =
+    if cfg.database.enable then config.services.postgresql.package else pkgs.postgresql;
 in
 {
   options.services.immich = {
@@ -265,7 +268,7 @@ in
       in
       [
         ''
-          ${lib.getExe' config.services.postgresql.package "psql"} -d "${cfg.database.name}" -f "${sqlFile}"
+          ${lib.getExe' postgresqlPackage "psql"} -d "${cfg.database.name}" -f "${sqlFile}"
         ''
       ];
 
@@ -333,7 +336,7 @@ in
       path = [
         # gzip and pg_dumpall are used by the backup service
         pkgs.gzip
-        config.services.postgresql.package
+        postgresqlPackage
       ];
 
       serviceConfig = commonServiceConfig // {