flake.lock: Update

Flake lock file updates:

• Updated input 'fenix':
    'github:nix-community/fenix/89a02ff13d98d54f0b3b41f9b8326eb26d7cdc2e' (2024-01-13)
  → 'github:nix-community/fenix/85f4139f3c092cf4afd9f9906d7ed218ef262c97' (2024-03-22)
• Updated input 'fenix/rust-analyzer-src':
    'github:rust-lang/rust-analyzer/9d8889cdfcc3aa0302353fc988ed21ff9bc9925c' (2024-01-11)
  → 'github:rust-lang/rust-analyzer/7ef7f442fc34b5eadb1c6ad6433bd6d0c51b056b' (2024-03-21)
• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/eabe8d3eface69f5bb16c18f8662a702f50c20d5' (2024-01-09)
  → 'github:NixOS/nixpkgs/20bc93ca7b2158ebc99b8cef987a2173a81cde35' (2024-03-23)
• Updated input 'utils':
    'github:numtide/flake-utils/4022d587cbbfd70fe950c1e2083a02621806a725' (2023-12-04)
  → 'github:numtide/flake-utils/b1d9ab70662946ef0850d488da1c9019f3a9752a' (2024-03-11)