RTD concurrency limit

[max-sixty]

What is your issue?

From #6472, and some PRs this weekend:

Is anyone familiar with what's going on with RTD? Did our concurrency limit drop?

Are there alternatives (e.g. running the tests on GHA even if the actual docs get built on RTD?). If we have to pay RTD for a subscription for a bit until we make changes then we could do that (I'm happy to given my recently poor contribution track-record!)

[max-sixty]

Looks like if we want to go to 6 concurrent builds, it's $250/ month: https://readthedocs.com/pricing/

This issue suggests others are having the same issue: readthedocs/readthedocs.org#9014, but that it's not intentional. So maybe let's see if it corrects.

The most important thing is that it doesn't keep retrying commits which are no longer the head of a branch — otherwise we could fall permanently behind. I know others have done some work to ensure GHA operates correctly here. Is anyone familiar with whether this happens in RTD?

[max-sixty]

This seems resolved now