Use `setup-python` just for caching

Description:
It would be good to be able to use this action just to cache dependencies, without also downloading Python. For example:

- uses: actions/setup-python@v5
  with:
    cache: pip

This currently doesn't work, because the version is not set.

You can do something similar with setup-node, for example:

- uses: actions/setup-node@v4
  with:
    cache: npm

Justification:
It would be able to use the existing logic in this action to cache dependencies, instead of having to use the cache action manually.

Are you willing to submit a PR?
Yes

先检查 action 的缓存处理和版本验证，然后对比 issue 中描述的 setup-node 行为。当 workflow 可以在不设置 Python 版本的情况下使用 cache: pip，并且有测试覆盖该配置时，即视为完成。