Looks like the bazel download mirror hasn't been populated with the 4.1.0 release.
I'm getting this warning:
WARNING: Download from https://mirror.bazel.build/github.com/bazelbuild/bazel-toolchains/archive/4.1.0.tar.gz failed: class com.google.devtools.build.lib.bazel.repository.downloader.UnrecoverableHttpException GET returned 404 Not Found
Context: https://github.com/grpc/grpc/pull/27410#discussion_r715420745
Looks like the bazel download mirror hasn't been populated with the 4.1.0 release.
I'm getting this warning: