Future versioning

[frenzymadness]

Because Fedora 34 is almost EOL and Fedora 35 does not contain Python 3.5, we have to find a way how to make it possible to use older versions of fedora-python-tox container image with this GH action. The necessary change of the container images itself is ready here: fedora-python/fedora-python-tox#57

Current usage: grep.app has found five users of @v0.4 and eighteen users of @master which both now means the latest container image.

Proposal:

1. Release version 34 of this action, hardcode the :34 manifest in it, and document that the versions are the same as the versions of underlying Fedora releases.
2. Wait for a while for the fedora-python-tox based on Fedora 35.
3. Switch the action to Fedora 35 and release version 35.
4. Add a changelog so users can easily identify what's new in the new version and decide whether they can switch or not.

If we need to change anything in the action itself, we can then release versions like 35.1.

[hroncok]

We could also use branches instead of tags, so when we actually fix something, users will get it automatically.

[frenzymadness]

I'd honestly rather use tags. Who wants the latest and greatest can always use the master branch. For others, it's IMHO better to have some control over the versions you use without automatic updates.

[hroncok]

Both work for me. We can start with tags and when we release 35.x for the n-th time, we might reconsider, or not. Not many changes were required here in the past, so I don't suspect we would need to "release" often.

[frenzymadness]

This is done. I'm gonna release v35.1 soon.