flake.lock: Update

Flake lock file updates:

• Updated input 'fenix':
    'github:nix-community/fenix/aaeaf4574767a0f5ed1787e990139aefcf4db103' (2024-03-30)
  → 'github:nix-community/fenix/0371cb3179c16f4f932557f855082bf57d371166' (2024-05-04)
• Updated input 'fenix/rust-analyzer-src':
    'github:rust-lang/rust-analyzer/f5a9250147f6569d8d89334dc9cca79c0322729f' (2024-03-29)
  → 'github:rust-lang/rust-analyzer/1a5bb27c018c947dab01ab70ffe1d267b0481a17' (2024-05-03)
• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/807c549feabce7eddbf259dbdcec9e0600a0660d' (2024-03-29)
  → 'github:NixOS/nixpkgs/5fd8536a9a5932d4ae8de52b7dc08d92041237fc' (2024-05-03)