Yanked `kem 0.3.0-pre.0` is required by latest stable version: `ml-kem 0.2.1`

[yezhizhen]

https://github.com/RustCrypto/KEMs/blob/c3325cf2c139907726f02e083d7d591a6a715131/ml-kem/Cargo.toml

The Servo CI is blocked as kem 0.3.0-pre.0 is just yanked. We tried to unblock it, servo/servo#42120 but ml-kem 0.2.1 is the latest official release in crates.io, which requires this yanked version.

[tarcieri]

Sorry, this is fallout from #2224. I unyanked that release.