Make codecov project check informational and only fail on patch check

[GDYendell]

If a change overall removes lines and those lines were all covered, project coverage will be reduced.

This should not be a failure if patch coverage is good. Ideally we would allow project coverage to fail only if patch coverage is 100%, but I don't think that is possible.

This can be configured in codevcov.yaml: https://docs.codecov.com/docs/commit-status

Thoughts?

[coretl]

Sounds reasonable to me, we already added a codecov.yaml to ophyd-async here:
https://github.com/bluesky/ophyd-async/blob/5a84d9293a26c28c2f319c315c530c852d46f75e/.codecov.yml#L1-L14

But I don't think we ignored project coverage as a check