deps: update petgraph requirement from 0.6 to 0.8

Updates the requirements on [petgraph](https://github.com/petgraph/petgraph) to permit the latest version.
- [Release notes](https://github.com/petgraph/petgraph/releases)
- [Changelog](https://github.com/petgraph/petgraph/blob/master/CHANGELOG.md)
- [Commits](https://github.com/petgraph/petgraph/compare/petgraph@v0.6.0...petgraph@v0.8.3)

---
updated-dependencies:
- dependency-name: petgraph
  dependency-version: 0.8.3
  dependency-type: direct:production
...

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

Author: dependabot[bot]

Cargo.lock

@@ -10,7 +10,7 @@ keywords.workspace = true
 categories.workspace = true
 
 [dependencies]
-petgraph      = { version = "0.6", features = ["serde-1"] }
+petgraph      = { version = "0.8", features = ["serde-1"] }
 serde         = { version = "1", features = ["derive"] }
 serde_json    = "1"
 tokio         = { version = "1", features = ["full"] }