Postgres until now has been using cirrus-ci for CI. Unfortunately they're shutting down June 1st.

They had been a good fit for us because:
- some free credits so everyone could run some CI on their own
- supported providing own compute for more demanding cases (via GCP and self hosted mac HW)
- jobs ran in one-off VMs
- support for custom images allowed us to pre-install everything, keeping test times manageable
- VMs not containers was good for perf
- CI job definitions could be run locally

@AndresFreundTec I would look at what curl is doing, and even ask @bagder
@renchap @AndresFreundTec the #curl project is fortunate to have GitHub as a sponsor so we get a lot of CI CPU in their infra for no money == we run most of our CI on GitHub
@bagder @renchap @AndresFreundTec doesn't GitHub offer unlimited CI usage for public repositories anyway? At least it did last time I checked a few months ago