Add ability to raise runtime warnings on reruns

[ssbarnea]

I want to make the reruns more visible on CI by making use of github actions annotations.

This can be achieved easily using a plugin like pytest-github-actions-annotate-failures/ which can also translated runtime warnings into github annotations.

Now the only thing we need is to be able to configure pytest-rerunfailures to raise runtime warnings when it does reruns, so they will be visible.

AFAIK there is no option to hook into how reruns are made to make this happen.

[icemac]

Is it needed to the requested changes here in pytest-rerunfailures or could there also be another place? I am asking because this seems to be a very special feature and I am a bit afraid of more feature creep here.

If other people think this is a valuable feature we'd need here, please speak up.

[webknjaz]

@icemac looks like you're being asked for just a conditional warnings.warn(). Though, I'd be careful with that since a lot of people would be running with filterwarnings = error making warnings explode.