[REQ] Let's make our GitHub Actions carbon-aware!

[julian-st]

Is your feature request related to a problem? Please describe.
This repos GitHub Actions uses ubuntu-latest but using this tag runs all the jobs in Azure (high-grid intensity) regions ... cough cough (350gCO2/kWh). We can make this better, more carbon-aware.

Describe the solution you'd like
Swap the runs-on tag to CarbonRunner's carbon-aware runner at least for ubuntu-latest and ubuntu-24.04. Finding the most low-carbon region and runs your jobs there. It saves 90% of emissions, 25% per minute cost (free for open-source projects) and is 40% faster than GitHub.