flake.lock: Update

Flake lock file updates:

• Updated input 'fenix':
    'github:nix-community/fenix/668102037129923cd0fc239d864fce71eabdc6a3' (2024-02-01)
  → 'github:nix-community/fenix/b03d2939685937a327f17df832bf9e8944ed9e3a' (2024-02-02)
• Updated input 'fenix/rust-analyzer-src':
    'github:rust-lang/rust-analyzer/42cb1a2bd79af321b0cc503d2960b73f34e2f92b' (2024-01-31)
  → 'github:rust-lang/rust-analyzer/850ba2fb6395cb39edef263256f7ba334f9142dc' (2024-02-01)
• Updated input 'nixpkgs-unstable':
    'github:NixOS/nixpkgs/97b17f32362e475016f942bbdfda4a4a72a8a652' (2024-01-29)
  → 'github:NixOS/nixpkgs/b8b232ae7b8b144397fdb12d20f592e5e7c1a64d' (2024-01-31)
• Updated input 'nurpkgs':
    'github:nix-community/NUR/c290e9ada7a920be104e37c3052b0c142eb3157d' (2024-02-02)
  → 'github:nix-community/NUR/9c02dedaf63decb814dabd377b22b40735287488' (2024-02-03)