flake.lock: Update

Flake lock file updates:

• Updated input 'circt-src':
    'github:llvm/circt/8acaeb5941e527c405c5166bedfccd96f2db3277' (2024-04-29)
  → 'github:llvm/circt/61b360ab4f97cdbec0fd59ff37440dfe82cd7a93' (2024-04-29)
• Updated input 'llvm-submodule-src':
    'github:llvm/llvm-project/418bdb49a758a5b3a128781a819b4e160521b7ed' (2024-04-24)
  → 'github:llvm/llvm-project/c4c8d08b81e622529aaf0bfc3020d2b9e87267b3' (2024-04-29)
• Updated input 'slang-src':
    'github:MikePopoloski/slang/de7c88b833ed4af529d2557642374c10bd7205bd' (2024-04-29)
  → 'github:MikePopoloski/slang/3ab3381d82a427de3728105c95782ef3f066940f' (2024-04-30)