build(deps): bump msgpack from 1.0.5 to 1.2.1 in /loadtesting (#1134)

Bumps [msgpack](https://github.com/msgpack/msgpack-python) from 1.0.5 to 1.2.1.
- [Release notes](https://github.com/msgpack/msgpack-python/releases)
- [Changelog](https://github.com/msgpack/msgpack-python/blob/main/CHANGELOG.md)
- [Commits](msgpack/msgpack-python@v1.0.5...v1.2.1)

---
updated-dependencies:
- dependency-name: msgpack
  dependency-version: 1.2.1
  dependency-type: indirect
...

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Author: dependabot[bot]