feat: Use elaborate errors value from API response if available

[whisperity]

This patch turns a "validation error"
(https://docs.github.com/en/rest/using-the-rest-api/troubleshooting-the-rest-api#validation-failed) such as a "too long description" into an understandable "too long description" issue in the CI logs, instead of a simple "Validation failed" print-out.

Uses the corresponding structure from gh api:

{
  "message": "Validation Failed",
  "errors": "Validation failed: Description is too long (maximum is 140 characters)",
  "documentation_url": "https://docs.github.com/rest/commits/statuses#create-a-commit-status",
  "status": "422"
}