Pipeline failures due to apparently outdated pyenv

[abingham]

See e.g. https://github.com/sixty-north/venv-management/actions/runs/11400518062

We've asked pyenv-action for a response: gabrielfalcao/pyenv-action#450

[rob-smallshire]

In the log we see an error no installed versions match the prefix -f.

This error is referenced at pyenv/pyenv-virtualenv#488 and pyenv/pyenv-virtualenv#487

The fix is apparently to upgrade to pyenv 2.4.8.

[rob-smallshire]

I've worked around this in 392c2f3 and de01a66 by using the latest version of the pyenv-action repo by specifying "gabrielfalcao/pyenv-action@main" as the action name. The code in the repo works, currently.