CNCF-paid GitHub Actions runners

[maelvls]

In case we need to use more GitHub Actions minutes, or larger runners, the CNCF can provide us with runners. This is especially important since we plan to migrate away from Google Cloud Build in order to migrate cert-manager to Makefile Modules in cert-manager/cert-manager#7718.

For context, in October 2025, we were only using about 20% of our free minutes allowance:

Here is the ticket I opened on the CNCF service desk: https://cncfservicedesk.atlassian.net/servicedesk/customer/portal/1/CNCFSD-3014