fix(attic): specify PostgreSQL database for postStart script

- Update `psql` command in the `postStart` script to explicitly connect to the `postgres` database before altering ownership of the `attic` database.
- Ensures the command runs without issues in environments with restricted default database access.

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 -d postgres -tAc 'ALTER DATABASE "attic" OWNER TO "atticd"'
   '';
 
   environment.systemPackages = with pkgs; [ attic-client ];