Bump nix from 0.25.0 to 0.26.2 in /src/agent

Bumps [nix](https://github.com/nix-rust/nix) from 0.25.0 to 0.26.2.
- [Release notes](https://github.com/nix-rust/nix/releases)
- [Changelog](https://github.com/nix-rust/nix/blob/v0.26.2/CHANGELOG.md)
- [Commits](nix-rust/nix@v0.25.0...v0.26.2)

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

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

src/agent/onefuzz-agent/Cargo.toml

@@ -35,7 +35,7 @@ dynamic-library = { path = "../dynamic-library" }
 
 [target.'cfg(target_family = "unix")'.dependencies]
 users = "0.11"
-nix = "0.25"
+nix = "0.26"
 
 [target.'cfg(target_family = "windows")'.dependencies]
 winapi = "0.3"

src/agent/onefuzz/Cargo.toml

@@ -55,7 +55,7 @@ winapi = { version = "0.3", features = ["impl-default", "psapi"] }
 
 [target.'cfg(target_family = "unix")'.dependencies]
 cpp_demangle = "0.4"
-nix = "0.25"
+nix = "0.26"
 
 [target.'cfg(target_os = "linux")'.dependencies]
 pete = "0.9"