Update petgraph requirement from 0.6.5 to 0.7.0

Updates the requirements on [petgraph](https://github.com/petgraph/petgraph) to permit the latest version.
- [Changelog](https://github.com/petgraph/petgraph/blob/master/RELEASES.rst)
- [Commits](https://github.com/petgraph/petgraph/compare/[email protected]@v0.7.0)

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

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

libcnb-package/Cargo.toml

@@ -20,7 +20,7 @@ ignore = "0.4.23"
 indoc = "2.0.5"
 libcnb-common.workspace = true
 libcnb-data.workspace = true
-petgraph = { version = "0.6.5", default-features = false }
+petgraph = { version = "0.7.0", default-features = false }
 thiserror = "2.0.6"
 uriparse = "0.6.4"
 which = "7.0.0"