flake.lock: Update (#16)

Flake lock file updates:

• Updated input 'fenix':
    'github:nix-community/fenix/53c3f9853aeaeb5a5ecba82527399fd0200feed0' (2023-04-21)
  → 'github:nix-community/fenix/6424d70f13761c203dada9de6ce417fc9f22712d' (2023-04-22)
• Updated input 'fenix/rust-analyzer-src':
    'github:rust-lang/rust-analyzer/0289dfa2611a605975e10dab6d3931c21509f90c' (2023-04-20)
  → 'github:rust-lang/rust-analyzer/af3b6a0893cc3a05b5ddc1e9d31b2c454b480426' (2023-04-21)
• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/39fa012bf8104323f89e62a293de90aebd0a6672' (2023-04-16)
  → 'github:NixOS/nixpkgs/ee7ec1c71adc47d2e3c2d5eb0d6b8fbbd42a8d1c' (2023-04-22)

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>