Obviously the Gitea API can return errors, which are also JSON strings.
Theres a new error response struct to collect these, and an enum for
Serde to unpack which ever variant happens to come back.
The API token is read from the environment variable `RELEASE_KEY_GITEA`.
"GITEA" is on the end because Gitea itself will refuse to allow users to
configure Act variables starting with the name "GITEA_".
All information about the release is hard-coded right now. I just needed
to see it hit the API and appear on the Gitea page. Hooking up the extra
options is up next.
