nixos/postgresql-backup: do not enable assertions when module is disabled

nixos/modules/services/backup/postgresql-backup.nix

@@ -152,7 +152,8 @@ in
 
   };
 
-  config = lib.mkMerge [
+  config = lib.mkIf cfg.enable (
+    lib.mkMerge [
       {
         assertions = [
           {
@@ -167,16 +168,17 @@ in
             message = "config.services.postgresqlBackup.compressionLevel must be set between 1 and 9 for gzip and 1 and 19 for zstd";
           }
         ];
-    }
-    (lib.mkIf cfg.enable {
+
         systemd.tmpfiles.rules = [
           "d '${cfg.location}' 0700 postgres - - -"
         ];
-    })
-    (lib.mkIf (cfg.enable && cfg.backupAll) {
+      }
+
+      (lib.mkIf cfg.backupAll {
         systemd.services.postgresqlBackup = postgresqlBackupService "all" "pg_dumpall ${cfg.pgdumpOptions}";
       })
-    (lib.mkIf (cfg.enable && !cfg.backupAll) {
+
+      (lib.mkIf (!cfg.backupAll) {
         systemd.services = lib.listToAttrs (
           map (
             db:
@@ -190,7 +192,8 @@ in
           ) cfg.databases
         );
       })
-  ];
+    ]
+  );
 
   meta.maintainers = with lib.maintainers; [ Scrumplex ];
 }