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
...

Signed-off-by: dependabot[bot] <support@github.com>

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

benches/Cargo.toml

@@ -8,7 +8,7 @@ license = "MIT"
 publish = false
 
 [dependencies]
-pprof = { version = "0.7", features = ["flamegraph", "criterion"] }
+pprof = { version = "0.8", features = ["flamegraph", "criterion"] }
 criterion = { version = "0.3", features = ["async_tokio", "html_reports"] }
 futures-channel = "0.3.15"
 futures-util = "0.3.15"