ci(smoke): read main SHA from the commits list endpoint

/commits/main returns 404 on this Gitea; use /commits?limit=1 and parse the
first sha with python instead of a greedy sed.

.gitea/workflows/prod-smoke.yml

@@ -55,8 +55,8 @@ jobs:
           fi
           expected="$(curl -fsS --max-time 15 \
             -H "Authorization: token ${SIAX_CI_TOKEN}" \
-            https://git.siax.io/api/v1/repos/admin/0pt/commits/main \
-            | sed -n 's/.*"sha":"\([0-9a-f]*\)".*/\1/p')"
+            "https://git.siax.io/api/v1/repos/admin/0pt/commits?limit=1" \
+            | python3 -c 'import sys,json; print(json.load(sys.stdin)[0]["sha"])')"
           echo "running=$running expected(main)=$expected"
           [ -n "$expected" ] || { echo "::error::could not read main SHA from Gitea"; exit 1; }
           [ "$running" = "$expected" ] || {