msgpack-c [renamed](https://github.com/msgpack/msgpack-c/blob/c_master/CHANGELOG.md#2023-03-02-version-600) their pkg-config file / shared library to msgpack-c in 6.0.0. There's an existing [PR](https://github.com/tmate-io/tmate/pull/281) to fix this for tmate, but the same would apply here.
