Update num_enum requirement from 0.6.0 to 0.7.0 (#42)

Updates the requirements on [num_enum](https://github.com/illicitonion/num_enum) to permit the latest version.
- [Commits](https://github.com/illicitonion/num_enum/commits)

---
updated-dependencies:
- dependency-name: num_enum
  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

@@ -30,7 +30,7 @@ kem-x25519-hkdf-sha256 = ["hpke/x25519"]
 
 [dependencies]
 rand = "0.8.5"
-num_enum = "0.6.0"
+num_enum = "0.7.0"
 cfg-if = "1.0.0"
 hpke = { version = "0.10.0", default-features = false, features = ["std"] }
 zeroize = "1.3"