examples in examples/toolchains use a platform provided cc toolchain

[prednaz]

Describe the bug
i believe, the examples in examples/toolchains use a platform provided cc toolchain instead of a rules_nixpkgs provided one, as claimed by #286.

To Reproduce
executing cd examples/toolchains/go && nix-shell --command 'bazel run --config=nix :hello' on nixos fails with Auto-Configuration Error: Cannot find gcc or CC; either correct your path or set the CC environment variable.

turning nix-shell into nix-shell --pure in .github/workflows/workflow.yaml causes ci to fail with the same error message too as demonstrated with #500.

Expected behavior
if the cc toolchain was provided by rules_nixpkgs, switching to nixos or nix-shell --pure should not prevent bazel from finding "gcc or CC".

Environment

• OS name + version: NixOS 23.11.4080.fb0c047e30b6 (Tapir) x86_64
• Version of the code: 126e9f6