Update hpke requirement from 0.11.0 to 0.12.0 (#60)

Updates the requirements on [hpke](https://github.com/rozbb/rust-hpke) to permit the latest version.
- [Changelog](https://github.com/rozbb/rust-hpke/blob/main/CHANGELOG.md)
- [Commits](https://github.com/rozbb/rust-hpke/commits)

---
updated-dependencies:
- dependency-name: hpke
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Cargo.toml

@@ -32,7 +32,7 @@ kem-x25519-hkdf-sha256 = ["hpke/x25519"]
 rand = "0.8.5"
 num_enum = "0.7.0"
 cfg-if = "1.0.0"
-hpke = { version = "0.11.0", default-features = false, features = ["std"] }
+hpke = { version = "0.12.0", default-features = false, features = ["std"] }
 zeroize = "1.6"
 
 [dependencies.serde_crate]