Fix CI impacted by Bazel 9 release

[rdesgroppes]

CI jobs on macOS started failing right after Bazel 9 release, see for instance: https://buildkite.com/bazel/rules-pkg/builds/4233/steps/canvas

Would you consider reviewing the following fix, please?

• fix(ci): use own md5 tool for Bazel 9 compatibility #1007