adpated for pandoc < 3, no arg

.gitea/workflows/pandoc.yaml

@@ -15,6 +15,6 @@ jobs:
         run: |
           for markdown in *md
           do
-              pandoc --self-contained=true --standalone --css pandoc.css -o "${markdown}.html" "${markdown}"
+              pandoc --self-contained --standalone --css pandoc.css -o "${markdown}.html" "${markdown}"
           done
       - run: echo "This job's status is ${{ job.status }}."