Bump the libcnb group with 3 updates

Bumps the libcnb group with 3 updates: [libcnb](https://github.com/heroku/libcnb.rs), [libherokubuildpack](https://github.com/heroku/libcnb.rs) and [libcnb-test](https://github.com/heroku/libcnb.rs).


Updates `libcnb` from 0.15.0 to 0.16.0
- [Release notes](https://github.com/heroku/libcnb.rs/releases)
- [Changelog](https://github.com/heroku/libcnb.rs/blob/main/CHANGELOG.md)
- [Commits](heroku/libcnb.rs@v0.15.0...v0.16.0)

Updates `libherokubuildpack` from 0.15.0 to 0.16.0
- [Release notes](https://github.com/heroku/libcnb.rs/releases)
- [Changelog](https://github.com/heroku/libcnb.rs/blob/main/CHANGELOG.md)
- [Commits](heroku/libcnb.rs@v0.15.0...v0.16.0)

Updates `libcnb-test` from 0.15.0 to 0.16.0
- [Release notes](https://github.com/heroku/libcnb.rs/releases)
- [Changelog](https://github.com/heroku/libcnb.rs/blob/main/CHANGELOG.md)
- [Commits](heroku/libcnb.rs@v0.15.0...v0.16.0)

---
updated-dependencies:
- dependency-name: libcnb
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: libcnb
- dependency-name: libherokubuildpack
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: libcnb
- dependency-name: libcnb-test
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: libcnb
...

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

Cargo.toml

@@ -10,8 +10,8 @@ rust-version = "1.66"
 flate2 = { version = "1", default-features = false, features = ["zlib"] }
 # libcnb has a much bigger impact on buildpack behaviour than any other dependencies,
 # so it's pinned to an exact version to isolate it from lockfile refreshes.
-libcnb = "=0.15.0"
-libherokubuildpack = { version = "=0.15.0", default-features = false, features = ["log"] }
+libcnb = "=0.16.0"
+libherokubuildpack = { version = "=0.16.0", default-features = false, features = ["log"] }
 regex = "1"
 semver = "1"
 serde = "1"
@@ -24,4 +24,4 @@ toml = "0.8"
 ureq = { version = "2", features = ["json"] }
 
 [dev-dependencies]
-libcnb-test = "=0.15.0"
+libcnb-test = "=0.16.0"