Erdős Problem 57: status mismatch (repo=solved, erdosproblems.com=formally solved)

The status of [Erdős problem 57](https://www.erdosproblems.com/57) appears to have changed.

- **[This repo](http://github.com/google-deepmind/formal-conjectures/blob/main/FormalConjectures/ErdosProblems/57.lean)**: `solved` (in `FormalConjectures/ErdosProblems/57.lean`)
- **[erdosproblems.com/57](https://www.erdosproblems.com/57)**: `formally solved`

Please verify and update the `@[category research ...]` annotation if appropriate.

Open FormalConjectures/ErdosProblems/57.lean and inspect its @[category research ...] annotation. Compare the repository status with the linked Erdős Problems page, verify whether the status has changed, and update the annotation if appropriate; done means the two status records agree.

Written by the indexing model from the issue text.