Mention '@bazel_tools' in the extract script

tools/remote-toolchains/extract-bazel-auto-toolchains.sh

@@ -1,7 +1,10 @@
 #!/usr/bin/env bash
+
 # This script executes Bazel inside a docker image to generate repositories
 # with a C++ toolchain definition. Those files can then be used when running
-# remote execution towards that image.
+# remote execution towards that image. This extracts the `@bazel_tools`
+# repository with toolchain definitions from Bazel. The version is taken from
+# `.bazelversion` in the repository root.
 #
 # Example usage: ./extract-bazel-auto-toolchains.sh ubuntu-act-22-04 ghcr.io/catthehacker/ubuntu:act-22.04
 set -eEuo pipefail
@@ -10,10 +13,22 @@ script_dir="$(dirname "${BASH_SOURCE[0]}")"
 
 bazel_version=$(cat "${script_dir}/../../.bazelversion")
 fixture_dir="$(realpath "${script_dir}/extract-bazel-auto-toolchains-fixture")"
-output_dir="$1"
-docker_image="$2"
+
+run() {
+    local -
+    set -x
+
+    docker run \
+        --rm \
+        -v "${fixture_dir}:/work" \
+        --workdir /work "$docker_image" \
+        /work/doit.sh "$bazel_version" | tar -C "$output_dir" -xz
+}
+
+output_dir="$1"; shift
+docker_image="$1"; shift
 
 mkdir -p "$output_dir"
-docker run --rm -v "${fixture_dir}:/work" --workdir /work "$docker_image" /work/doit.sh "$bazel_version" | tar -C "$output_dir" -xz
+run
 
 echo "Files successfully extracted the toolchain to ${output_dir}" 1>&2