Upgrade CI to bazel 4.0.0

[pcj]

No description provided.

[pcj]

(14:06:51) ERROR: /workdir/tests/contrib/BUILD:172:21: Action tests/contrib/derivative_with_volume_repro_test_test_img1_outs failed: (Exit 1): derivative_with_volume_repro_test.build1 failed: error executing command
--
  | (cd /var/lib/buildkite-agent/.cache/bazel/_bazel_buildkite-agent/ec321eb2cc2d0f8f91b676b6d4c66c29/sandbox/linux-sandbox/1412/execroot/io_bazel_rules_docker && \
  | exec env - \
  | PATH=/var/lib/buildkite-agent/.cache/bazelisk/downloads/bazelbuild/bazel-4.1.0-linux-x86_64/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/opt/go1.15.2.linux-amd64/bin:/opt/swift-5.2.5-RELEASE-ubuntu18.04/usr/bin \
  | bazel-out/k8-fastbuild/bin/tests/contrib/derivative_with_volume_repro_test.build1)
  | Execution platform: @local_config_platform//:host
  |  
  | Use --sandbox_debug to see verbose messages from the sandbox
  | Loaded image: bazel/tests/contrib:derivative_with_volume_repro_test
  | ERROR: The project you're trying to build requires Bazel 4.1.0 (specified in /workdir/.bazelversion), but it wasn't found in /usr/local/lib/bazel/bin.
  |