Read a GitHub check's log

Returns one UTF-8 excerpt of the job log of a GitHub Actions check run this repository mirrors from GitHub, in the shape of a CI job log excerpt (tailBytes, or startByte and endByte), with the check's name and result. GitCafe keeps no GitHub log: each request reads it from GitHub with the repository's GitHub App installation (it needs Actions read permission), so it is slower than a CI job log. The check id is the GitHub check run id (checks.contexts[].url of the pull request status ends in /runs/<id>). GitHub keeps no log for a check run from another app: that is the problem ci-logs-github-not-actions, whose url is the check's GitHub page. That, a job that has not finished and a log GitHub no longer keeps are problems, never an empty log; logs over 64 MiB are refused. Public repositories allow anonymous reads; supplied credentials are validated and may expand access to private resources.