[release/6.0] (deps): Bump src/submodules/MessagePack-CSharp (#48003)

Bumps [src/submodules/MessagePack-CSharp](https://github.com/aspnet/MessagePack-CSharp) from `6caf299` to `ecc4e18`.
- [Release notes](https://github.com/aspnet/MessagePack-CSharp/releases)
- [Commits](aspnet/MessagePack-CSharp@6caf299...ecc4e18)

---
updated-dependencies:
- dependency-name: src/submodules/MessagePack-CSharp
  dependency-type: direct:production
...

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

Author: dependabot[bot]