build(deps): update proptest-derive requirement from 0.7 to 0.8

Updates the requirements on [proptest-derive](https://github.com/proptest-rs/proptest) to permit the latest version.
- [Release notes](https://github.com/proptest-rs/proptest/releases)
- [Changelog](https://github.com/proptest-rs/proptest/blob/main/CHANGELOG.md)
- [Commits](proptest-rs/proptest@proptest-derive-0.7.0...proptest-derive-0.8.0)

---
updated-dependencies:
- dependency-name: proptest-derive
  dependency-version: 0.8.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

cdevents-sdk/Cargo.toml

@@ -14,7 +14,7 @@ cloudevents-sdk = { version = "0.9", optional = true, default-features = false }
 enum_dispatch = "0.3"
 fluent-uri = { version = "0.4", features = ["serde"] }
 proptest = { version = "1", optional = true }
-proptest-derive = { version = "0.7", optional = true }
+proptest-derive = { version = "0.8", optional = true }
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 thiserror = "2"