Bump nix from 0.26.4 to 0.29.0

Bumps [nix](https://github.com/nix-rust/nix) from 0.26.4 to 0.29.0.
- [Changelog](https://github.com/nix-rust/nix/blob/master/CHANGELOG.md)
- [Commits](nix-rust/nix@v0.26.4...v0.29.0)

---
updated-dependencies:
- dependency-name: nix
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Cargo.toml

@@ -26,7 +26,7 @@ backtrace = { version = "0.3" }
 once_cell = "1.9"
 libc = "^0.2.66"
 log = "0.4"
-nix = { version = "0.26", default-features = false, features = ["signal", "fs"] }
+nix = { version = "0.29", default-features = false, features = ["signal", "fs"] }
 parking_lot = "0.12"
 tempfile = "3.1"
 thiserror = "1.0"