bazel: bump rules_python to 2.3.1

The microbench CI job re-fetches the python toolchain
before all but the first of its 46 `bazel run` invocations,
warning each time:

  WARNING: Repository '@@rules_python++python+python_3_12_aarch64-unknown-linux-gnu'
  will be fetched again since the file 'lib/python3.12' has been modified
  externally. External modifications can lead to incorrect builds.

This happens because CI runs it as root, and some .pyc files get written into
the hermetic (bazel managed) python sys root. This is fixed in 2.3.1, so update.

Fixes CORE-17095.