Update nix requirement from 0.25 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@v0.25.0...v0.26.1)

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

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

Author: dependabot[bot]

Cargo.toml

@@ -14,7 +14,7 @@ rust-version = "1.60"
 
 [dependencies]
 comma = "1.0"
-nix = "0.25"
+nix = "0.26"
 regex = "1"
 tempfile = "3"
 thiserror = "1.0.34"