docs: fix typo in cache policy comment (#2740)

## Summary

Correct the spelling of `mistakenly` in the comment explaining the
legacy
`cache` alias for `cachePolicy`.

No runtime behavior or public API changes.

## Testing

- `pnpm dlx oxfmt@0.42.0 --check libs/langgraph-core/src/func/index.ts`
- `git diff --check`

Comment-only change. No tests or changeset required.