build(deps): update jsonschema requirement from 0.18.0 to 0.21.0

Updates the requirements on [jsonschema](https://github.com/Stranger6667/jsonschema-rs) to permit the latest version.
- [Release notes](https://github.com/Stranger6667/jsonschema-rs/releases)
- [Changelog](https://github.com/Stranger6667/jsonschema-rs/blob/master/CHANGELOG.md)
- [Commits](Stranger6667/jsonschema@rust-v0.18.0...rust-v0.21.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

Cargo.toml

@@ -30,7 +30,7 @@ oci-spec = { version = "0.6.6", features = ["runtime"] }
 anyhow = "1.0"
 clap = "4.5.4"
 serde_json = "1.0"
-jsonschema = "0.18.0"
+jsonschema = "0.21.0"
 once_cell = "1.8.0"
 notify = "6.1.1"
 serde = "1.0.131"