message: Add checksum to external pybind11 archive.
diff: @@ -23,6 +23,7 @@ def tink_py_deps():
  build_file = "@pybind11_bazel//:pybind11.BUILD",
  strip_prefix = "pybind11-2.4.3",
  urls = ["https://github.com/pybind/pybind11/archive/v2.4.3.tar.gz"],
  + sha256 = "1eed57bc6863190e35637290f97a20c81cfe4d9090ac0a24f3bbf08f265eb71d",
  )
  if not native.existing_rule("pybind11_bazel"):
  