Pin python 3.8 and 3.9 at patch level

[csmarchbanks]

Something around the upgrade of these images caused our pipeline to begin to fail. For example https://app.circleci.com/pipelines/github/prometheus/client_python/589/workflows/26c0f218-1bfb-40b7-99ba-b9725699da07/jobs/6025.

py3.8: internal error
Traceback (most recent call last):
  File "/home/circleci/.local/lib/python3.8/site-packages/tox/session/cmd/run/single.py", line 45, in _evaluate
    tox_env.setup()
  File "/home/circleci/.local/lib/python3.8/site-packages/tox/tox_env/api.py", line 249, in setup
    self._setup_env()
  File "/home/circleci/.local/lib/python3.8/site-packages/tox/tox_env/python/runner.py", line 106, in _setup_env
    super()._setup_env()
  File "/home/circleci/.local/lib/python3.8/site-packages/tox/tox_env/python/api.py", line 198, in _setup_env
    self.ensure_python_env()
  File "/home/circleci/.local/lib/python3.8/site-packages/tox/tox_env/python/api.py", line 202, in ensure_python_env
    conf = self.python_cache()
  File "/home/circleci/.local/lib/python3.8/site-packages/tox/tox_env/python/virtual_env/api.py", line 77, in python_cache
    base = super().python_cache()
  File "/home/circleci/.local/lib/python3.8/site-packages/tox/tox_env/python/api.py", line 240, in python_cache
    "version_info": list(self.base_python.version_info),
  File "/home/circleci/.local/lib/python3.8/site-packages/tox/tox_env/python/api.py", line 250, in base_python
    self._base_python = self._get_python(base_pythons)
  File "/home/circleci/.local/lib/python3.8/site-packages/tox/tox_env/python/virtual_env/api.py", line 134, in _get_python
    interpreter = self.creator.interpreter
  File "/home/circleci/.local/lib/python3.8/site-packages/tox/tox_env/python/virtual_env/api.py", line 126, in creator
    return self.session.creator
  File "/home/circleci/.local/lib/python3.8/site-packages/tox/tox_env/python/virtual_env/api.py", line 107, in session
    self._virtualenv_session = session_via_cli(env_dir, options=None, setup_logging=False, env=env)
  File "/home/circleci/.local/lib/python3.8/site-packages/virtualenv/run/__init__.py", line 46, in session_via_cli
    parser, elements = build_parser(args, options, setup_logging, env)
  File "/home/circleci/.local/lib/python3.8/site-packages/virtualenv/run/__init__.py", line 72, in build_parser
    CreatorSelector(interpreter, parser),
  File "/home/circleci/.local/lib/python3.8/site-packages/virtualenv/run/plugin/creators.py", line 13, in __init__
    creators, self.key_to_meta, self.describe, self.builtin_key = self.for_interpreter(interpreter)
  File "/home/circleci/.local/lib/python3.8/site-packages/virtualenv/run/plugin/creators.py", line 20, in for_interpreter
    for key, creator_class in cls.options("virtualenv.create").items():
  File "/home/circleci/.local/lib/python3.8/site-packages/virtualenv/run/plugin/base.py", line 44, in options
    cls._OPTIONS = cls.entry_points_for(key)
  File "/home/circleci/.local/lib/python3.8/site-packages/virtualenv/run/plugin/base.py", line 23, in entry_points_for
    return OrderedDict((e.name, e.load()) for e in cls.entry_points().get(key, {}))
  File "/home/circleci/.local/lib/python3.8/site-packages/virtualenv/run/plugin/base.py", line 23, in <genexpr>
    return OrderedDict((e.name, e.load()) for e in cls.entry_points().get(key, {}))
  File "/home/circleci/.pyenv/versions/3.8.19/lib/python3.8/site-packages/setuptools/_vendor/importlib_metadata/__init__.py", line 210, in load
    return functools.reduce(getattr, attrs, module)
AttributeError: module 'virtualenv.create.via_global_ref.builtin.cpython.mac_os' has no attribute 'CPython3macOsBrew'
  py3.8: FAIL code 2 (0.01 seconds)
  evaluation failed :( (0.14 seconds)

Exited with code exit status 2

In the past we had to pin a version for virtualenv, but it is already pinned. My guess is this has to do with CircleCI-Public/cimg-python#240 which is in the 3.10+ versions, but not the latest 3.8 and 3.9 images. Hopefully at the next release of circleci images we can go back to just fixing the minor version.