chore: Add @nowarn annotation to LazyVals. (scala#22270)

Unsafe is planned to be removed in future  Java versions.

Motivication:

Makes it compile on JDK 23
refs: https://openjdk.org/jeps/471

Modification:
Add `@nowarn("cat=deprecation")`

Result:
Compiles successfully on JDK 23

Author: He-Pin