message: doc: Fix typo in LoadBlockIndex
diff: @@ -317,7 +317,7 @@ bool BlockManager::LoadBlockIndex(
  // because they will still be attached to the active chainstate if they
  // actually contain more work.
  //
  - // Instad of this height-based approach, an earlier attempt was made at
  + // Instead of this height-based approach, an earlier attempt was made at
  // detecting "holistically" whether the block index under consideration
  // relied on an assumed-valid ancestor, but this proved to be too slow to
  // be practical.
  