Automatically update flake.lock to the latest version

flake-utils  919d646de7 (2023-07-11) -> f9e7cf8183 (2023-08-23)
serokell-nix 851b937e52 (2023-08-03) -> 7503014062 (2023-09-05)
tzbot        c637be13b2 (2023-03-09) -> 4c2315ea7d (2023-09-05)