build(deps): update peg requirement from 0.6.3 to 0.8.4

Updates the requirements on [peg](https://github.com/kevinmehall/rust-peg) to permit the latest version.
- [Release notes](https://github.com/kevinmehall/rust-peg/releases)
- [Commits](kevinmehall/rust-peg@0.6.3...0.8.4)

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

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

varlink_parser/Cargo.toml

@@ -21,4 +21,4 @@ travis-ci = { repository = "varlink/rust" }
 [dependencies]
 colored = "2.1.0"
 thiserror = "2.0.3"
-peg = "0.6.3"
+peg = "0.8.4"