Amazon AWS will soon add support for the M1 hardware to the macOS EC2 managed offering announced a few weeks ago. AWS also offers free credits to prominent Open Source projects.

It's not available yet but it should be a good option once they become available, you can immediately start the process of applying for the credits.

This way you would get access to the required hardware without any costs and without having to maintain it. They are designed from the ground up towards such CI/development use cases.

You can also use the same credits for getting access to Intel and ARM Linux, as well as Windows EC2 instances. This may improve your project's CI and build times.

Disclaimer: I work at AWS.