Fix changlog extraction for GitHub release

The `--standalone` argument for pandoc caused it to treat the title (if
only one was in the document) as title metadata that was transformed to
a YAML frontmatter block.

.github/workflows/ci.yml

@@ -118,7 +118,7 @@ jobs:
 
       - uses: docker://pandoc/core:3
         with:
-          args: --standalone --wrap none -f rst -t gfm --output=release-body.md release-body.rst
+          args: --wrap none -f rst -t gfm --output=release-body.md release-body.rst
 
       - name: Create GitHub release
         uses: softprops/action-gh-release@v1