fix(attic): remove unused $PSQL alias in postStart script

- Replace `$PSQL` with `psql` to use the correct PostgreSQL CLI directly.
- Ensures compatibility and prevents potential runtime issues in the systemd service.

systems/x86_64-linux/attic/atticd.nix

@@ -12,7 +12,7 @@
   };
 
   systemd.services.postgresql.postStart = lib.mkAfter ''
-    $PSQL -tAc 'ALTER DATABASE "attic" OWNER TO "atticd"'
+    psql -tAc 'ALTER DATABASE "attic" OWNER TO "atticd"'
   '';
 
   environment.systemPackages = with pkgs; [ attic-client ];