Erdős Problem 63: status mismatch (repo=solved, erdosproblems.com=formally solved)

The status of [Erdős problem 63](https://www.erdosproblems.com/63) appears to have changed.

- **[This repo](http://github.com/google-deepmind/formal-conjectures/blob/main/FormalConjectures/ErdosProblems/63.lean)**: `solved` (in `FormalConjectures/ErdosProblems/63.lean`)
- **[erdosproblems.com/63](https://www.erdosproblems.com/63)**: `formally solved`

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

Start with FormalConjectures/ErdosProblems/63.lean and inspect its @[category research ...] annotation. Verify the current status against erdosproblems.com/63, then update the annotation if the external status is confirmed. Done means the repository status matches the verified status.

Written by the indexing model from the issue text.