build(deps): update cbindgen requirement from 0.27.0 to 0.28.0 (#361)

Updates the requirements on [cbindgen](https://github.com/mozilla/cbindgen) to permit the latest version.
- [Release notes](https://github.com/mozilla/cbindgen/releases)
- [Changelog](https://github.com/mozilla/cbindgen/blob/master/CHANGES)
- [Commits](mozilla/cbindgen@v0.27.0...0.28.0)

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

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

Author: dependabot[bot]

bindings/ffi/Cargo.toml

@@ -20,5 +20,5 @@ coverage = ["regorus/coverage"]
 custom_allocator = []
 
 [build-dependencies]
-cbindgen = "0.27.0"
+cbindgen = "0.28.0"
 csbindgen = "=1.9.3"