flake.lock: Update

Flake lock file updates:

• Updated input 'fenix':
    'github:nix-community/fenix/aaeaf4574767a0f5ed1787e990139aefcf4db103' (2024-03-30)
  → 'github:nix-community/fenix/297c756ba6249d483c1dafe42378560458842173' (2024-05-10)
• Updated input 'fenix/rust-analyzer-src':
    'github:rust-lang/rust-analyzer/f5a9250147f6569d8d89334dc9cca79c0322729f' (2024-03-29)
  → 'github:rust-lang/rust-analyzer/5bf2f85c8054d80424899fa581db1b192230efb5' (2024-05-09)
• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/807c549feabce7eddbf259dbdcec9e0600a0660d' (2024-03-29)
  → 'github:NixOS/nixpkgs/e4e7a43a9db7e22613accfeb1005cca1b2b1ee0d' (2024-05-11)