Update nix requirement from 0.24 to 0.26

Updates the requirements on [nix](https://github.com/nix-rust/nix) to permit the latest version.
- [Release notes](https://github.com/nix-rust/nix/releases)
- [Changelog](https://github.com/nix-rust/nix/blob/master/CHANGELOG.md)
- [Commits](nix-rust/nix@v0.24.0...v0.26.1)

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

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

Cargo.toml

@@ -48,7 +48,7 @@ url = "2"
 
 [target.'cfg(target_os = "linux")'.dev-dependencies]
 inotify = { version = "0.10", default-features = false }
-nix = "0.24"
+nix = "0.26"
 timerfd = "1"
 
 [target.'cfg(windows)'.dev-dependencies]