ci: a cancelled GitHub run no longer reports failure to Gitea

The mirror can push one commit twice in quick succession. GitHub then
starts two runs and cancels the older, and that run's report job posted
"failure" for the commit. Gitea's github job, seeing the newest status,
failed the check while the surviving run was still building and later
passed.

A cancelled run now posts nothing and leaves the result to the run that
superseded it. A real failure still reports failure.

.github/workflows/ci.yml

@@ -246,8 +246,12 @@ jobs:
     steps:
       - env:
           GITEA_TOKEN: ${{ secrets.GITEA_TOKEN }}
-          STATE: ${{ (contains(needs.*.result, 'failure') || contains(needs.*.result, 'cancelled')) && 'failure' || 'success' }}
+          STATE: ${{ contains(needs.*.result, 'failure') && 'failure' || (contains(needs.*.result, 'cancelled') && 'cancelled' || 'success') }}
         run: |
+          # A cancelled run was superseded by a newer run for the same commit (the
+          # mirror can push one commit twice); that run reports. Posting "failure"
+          # here would fail the Gitea check while the real build is still going.
+          if [ "$STATE" = cancelled ]; then echo "cancelled: leaving the result to the newer run"; exit 0; fi
           jq -n --arg s "$STATE" --arg c "$STATUS_CONTEXT" \
                 --arg u "$GITHUB_SERVER_URL/$GITHUB_REPOSITORY/actions/runs/$GITHUB_RUN_ID" \
                 '{state:$s, context:$c, target_url:$u, description:"GitHub Actions"}' \