Erdős Problem 254: status mismatch (repo=formally solved, erdosproblems.com=open)

The status of [Erdős problem 254](https://www.erdosproblems.com/254) appears to have changed.

- **[This repo](http://github.com/google-deepmind/formal-conjectures/blob/main/FormalConjectures/ErdosProblems/254.lean)**: `formally solved` (in `FormalConjectures/ErdosProblems/254.lean`)
- **[erdosproblems.com/254](https://www.erdosproblems.com/254)**: `open`

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

Start with FormalConjectures/ErdosProblems/254.lean and inspect its @[category research ...] annotation. Compare the repository's formalization status with the linked erdosproblems.com/254 page, then update the annotation if the status is verified; done means the two sources no longer contradict each other.

Written by the indexing model from the issue text.