update flake.lock

Should've been done in fe606f4f but the
author didn't realize it.

Flake lock file updates:

• Updated input 'rocksdb':
    'github:facebook/rocksdb/bcf88d48ce8aa8b536aee4dd305533b3b83cf435' (2024-04-16)
  → 'github:facebook/rocksdb/6f7cabeac80a3a6150be2c8a8369fcecb107bf43' (2024-04-22)