Share Runner Pipeline minutes running out

I’ve been running CI for one of my projects quite a bit lately, as it’s the only way I can debug some Windows-only failures. I just received an email saying:

Action required: Less than 30% of Pipeline minutes remain

And it includes a link to buy more pipeline minutes. Well, this is an open source project so I hope I don’t have to buy more minutes. Also, the link leads to a 404 page so I couldn’t even if I wanted to. It also doesn’t tell me if this is a lifetime limit of minutes, monthly, or whatever.

How can a small open source project acquire more runner minutes?