Update toml requirement from 0.7.6 to 0.8.0 (#688)

Updates the requirements on [toml](https://github.com/toml-rs/toml) to permit the latest version.
- [Commits](toml-rs/toml@toml-v0.7.6...toml-v0.7.8)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Cargo.toml

@@ -30,4 +30,4 @@ libcnb-data = { version = "=0.14.0", path = "libcnb-data" }
 libcnb-package = { version = "=0.14.0", path = "libcnb-package" }
 libcnb-proc-macros = { version = "=0.14.0", path = "libcnb-proc-macros" }
 libcnb-test = { version = "=0.14.0", path = "libcnb-test" }
-toml = { version = "0.7.6" }
+toml = { version = "0.8.0" }