chore(flake): update flake.lock

Flake lock file updates:

• Updated input 'emacs-overlay':
    'github:nix-community/emacs-overlay/2568557a13c8437acfe70164f664c9c0e6d1bb94' (2024-08-10)
  → 'github:nix-community/emacs-overlay/5b263d5788c503a83399c2b54ba87e46fb96b418' (2024-08-17)
• Updated input 'emacs-overlay/nixpkgs-stable':
    'github:NixOS/nixpkgs/21cc704b5e918c5fbf4f9fff22b4ac2681706d90' (2024-08-06)
  → 'github:NixOS/nixpkgs/c3d4ac725177c030b1e289015989da2ad9d56af0' (2024-08-15)
• Updated input 'melpa':
    'github:melpa/melpa/9875de56d4c4f5e1d6f127a0b2e408e87a9dd932' (2024-08-08)
  → 'github:melpa/melpa/8399712211a0fb927970917aec906a97488d00fb' (2024-08-11)
• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/23cbcfad3b2096470e5ab1faada54f1c4147f6e2' (2024-08-09)
  → 'github:NixOS/nixpkgs/b764d780d8af360061540651c3adf84895b5ff90' (2024-08-16)
• Updated input 'nongnu-elpa':
    'git+https://git.savannah.gnu.org/git/emacs/nongnu.git?ref=main&rev=f031337c6ee125455a98e2de899a563388e5de19' (2024-07-16)
  → 'git+https://git.savannah.gnu.org/git/emacs/nongnu.git?ref=main&rev=6a3a4692b78145de00a4c1ad345107bbf9160307' (2024-08-15)