Deploy PR to staging only if CI checks passed

Although there are various checks enabled in KernelCI repositories (e.g. https://github.com/kernelci/kernelci-pipeline/pull/643) it is not verified if they all passed before [adding a PR to the staging deployment](https://github.com/kernelci/kernelci-deploy/blob/8674f1b1bc77a8bc5349319e9fbd008060a80e1f/pending.py#L77).

PRs should be included in staging on condition that all CI checks passed.