Refactor commit status for Actions jobs (go-gitea#23786)

Before:
<img width="353" alt="xnip_230329_163852"
src="https://user-images.githubusercontent.com/9418365/228479807-424452df-10fa-45cf-ae4b-09939c0ed54c.png">
After:
<img width="508" alt="xnip_230329_163358"
src="https://user-images.githubusercontent.com/9418365/228479923-537b54fe-9564-4105-a068-bcc75fa2a7ea.png">

Highlights:
- Treat `StatusSkipped` as `CommitStatusSuccess` instead of
`CommitStatusFailure`, so it fixed go-gitea#23599.
- Use the bot user `gitea-actions` instead of the trigger as the creator
of commit status.
- New format `<run_name> / <job_name> / (<event>)` for the context of
commit status to avoid conflicts.
- Add descriptions for commit status.
- Add the missing calls to `CreateCommitStatus`.
- Refactor `CreateCommitStatus` to make it easier to use.