upgrade nix to 0.26.4

Summary:
I am upgrading nix to 0.29.0. To ensure each step produces clean CI
and is bisectable if something goes wrong, start by going from 0.25 to
0.26.4.

Reviewed By: zertosh

Differential Revision: D66275116

fbshipit-source-id: 63c87ff4f4c631061e5a1c721f52563dc90b7e2b

shed/slog_glog_fmt/Cargo.toml

@@ -30,7 +30,7 @@ regex = "1.9.2"
 thiserror = "1.0.64"
 
 [target.'cfg(target_os = "linux")'.dependencies]
-nix = "0.25"
+nix = "0.26.4"
 
 [target.'cfg(target_os = "macos")'.dependencies]
-nix = "0.25"
+nix = "0.26.4"