Update auto-update.yml

Fixes `Invalid value for "head"` error (https://github.com/iptv-org/iptv/actions/runs/3806696310/jobs/6476444023)
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f