Bump bumpalo from 3.9.1 to 3.12.0 in /rust/json-gen

Bumps [bumpalo](https://github.com/fitzgen/bumpalo) from 3.9.1 to 3.12.0.
- [Release notes](https://github.com/fitzgen/bumpalo/releases)
- [Changelog](https://github.com/fitzgen/bumpalo/blob/main/CHANGELOG.md)
- [Commits](fitzgen/bumpalo@3.9.1...3.12.0)

---
updated-dependencies:
- dependency-name: bumpalo
  dependency-type: indirect
...

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