flake: update inputs (#277)

Flake lock file updates:

• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/8a3354191c0d7144db9756a74755672387b702ba?narHash=sha256-Grh5PF0%2BgootJfOJFenTTxDTYPidA3V28dqJ/WV7iis%3D' (2024-08-18)
  → 'github:NixOS/nixpkgs/c374d94f1536013ca8e92341b540eba4c22f9c62?narHash=sha256-Z/ELQhrSd7bMzTO8r7NZgi9g5emh%2BaRKoCdaAv5fiO0%3D' (2024-08-21)
• Updated input 'nixpkgs-stable':
    'github:NixOS/nixpkgs/f1bad50880bae73ff2d82fafc22010b4fc097a9c?narHash=sha256-D5HwjQw/02fuXbR4LCTo64koglP2j99hkDR79/3yLOE%3D' (2024-08-19)
  → 'github:NixOS/nixpkgs/224042e9a3039291f22f4f2ded12af95a616cca0?narHash=sha256-HMpK7hNjhEk4z5SFg5UtxEio9OWFocHdaQzCfW1pE7w%3D' (2024-08-21)
• Updated input 'rust-overlay':
    'github:oxalica/rust-overlay/45e98fbd62c32e5927e952d2833fa1ba4fb35a61?narHash=sha256-L8dKaX4T3k%2BTR2fEHCfGbH4UXdspovz/pj87iai9qmc%3D' (2024-08-21)
  → 'github:oxalica/rust-overlay/6dc6d34a3a217457d7044dcce32b6d537480a6a1?narHash=sha256-x/XhOAszT/ejditCHUtGOjQcVg2AQhrC/QVew3i7kTI%3D' (2024-08-22)

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