When creating commit status for Actons jobs, a payload with nil
`HeadCommit` will cause panic.
Reported at:
https://gitea.com/gitea/act_runner/issues/28#issuecomment-732166
Although the `HeadCommit` probably can not be nil after #23215,
`CreateCommitStatus` should protect itself, to avoid being broken in the
future.
In addition, it's enough to print error log instead of returning err
when `CreateCommitStatus` failed.
---------
Co-authored-by: delvh <dev.lh@web.de>
47b912cd52