Bump tracing-core from 0.1.30 to 0.1.31 in /cmd/zfs_object_agent

Bumps [tracing-core](https://github.com/tokio-rs/tracing) from 0.1.30 to 0.1.31.
- [Release notes](https://github.com/tokio-rs/tracing/releases)
- [Commits](tokio-rs/tracing@tracing-core-0.1.30...tracing-core-0.1.31)

---
updated-dependencies:
- dependency-name: tracing-core
  dependency-type: indirect
  update-type: version-update:semver-patch
...

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