Hi, I'm seeing warnings building common projects that have the bazel-toolchains as a dependency because the following mirror.bazel.build URL is 404ing.

https://mirror.bazel.build/github.com/bazelbuild/bazel-toolchains/archive/3.2.0.tar.gz

An example of one project whose bazel build process is displaying warnings about this is the @google Tink project:
https://github.com/google/tink/blob/23ce810c979b1105fe6a657a5667a7275764b411/tink_base_deps.bzl#L69-L79

This is the error I see:

$ git clone https://github.com/google/tink
$ cd tink/tools/tinkey
$ bazel build tinkey
WARNING: Download from https://mirror.bazel.build/github.com/bazelbuild/bazel-toolchains/archive/3.2.0.tar.gz failed: class com.google.devtools.build.lib.bazel.repository.downloader.UnrecoverableHttpException GET returned 404 Not Found
...

According to the releases page the bazel-toolchains (link below) is supposed to be available at two URLs, one being the mirror, but it seems the mirror is missing version 3.2.0.

https://releases.bazel.build/bazel-toolchains.html

Is the mirror being maintained?

Should we continue to use the mirror as a dependency location?