chore(deps): update pprof requirement from 0.7 to 0.8 (#732)

Updates the requirements on [pprof](https://github.com/tikv/pprof-rs) to permit the latest version.
- [Release notes](https://github.com/tikv/pprof-rs/releases)
- [Changelog](https://github.com/tikv/pprof-rs/blob/master/CHANGELOG.md)
- [Commits](https://github.com/tikv/pprof-rs/commits)

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

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