build(deps): bump bedrock2 from 81daba5 to a7857fd

Bumps [bedrock2](https://github.com/mit-plv/bedrock2) from `81daba5` to `a7857fd`.
- [Release notes](https://github.com/mit-plv/bedrock2/releases)
- [Commits](mit-plv/bedrock2@81daba5...a7857fd)

---
updated-dependencies:
- dependency-name: bedrock2
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>