flake.lock: Update

Flake lock file updates:

• Updated input 'flake-utils':
    'github:numtide/flake-utils/a1720a10a6cfe8234c0e93907ffe81be440f4cef' (2023-05-31)
  → 'github:numtide/flake-utils/919d646de7be200f3bf08cb76ae1f09402b6f9b4' (2023-07-11)
• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/e635192892f5abbc2289eaac3a73cdb249abaefd' (2023-06-01)
  → 'github:NixOS/nixpkgs/2a9d660ff0f7ffde9d73be328ee6e6f10ef66b28' (2023-07-28)
• Updated input 'rust-overlay':
    'github:oxalica/rust-overlay/c535b4f3327910c96dcf21851bbdd074d0760290' (2023-06-03)
  → 'github:oxalica/rust-overlay/5c06b0ed7bfb00f3a925af6c4acd1636596381c1' (2023-07-29)