Put nightly CI for IBM SEL into CoCo dashboard

[BbolroC]

Which feature do you think can be improved?

ATM, the dashboard only tracks CI jobs in https://github.com/kata-containers/kata-containers/actions/workflows/ci-nightly.yaml, but those for IBM SEL are located in https://github.com/kata-containers/kata-containers/actions/workflows/ci-nightly-s390x.yaml
I would be good to get those jobs in the dashboard to track all TEE CI jobs in one place.