Fix GitHub release notes parsing

Author: mkrnr

.github/workflows/ci/helpers.sh

@@ -151,11 +151,13 @@ EOF
   done
   run pandoc --from=gfm --to=gfm \
     --lua-filter=.github/RELEASE_DRAFT_FILTER.lua \
-    --template=.github/RELEASE_DRAFT_TEMPLATE.md \
-    --shift-heading-level-by=1 --wrap=none \
-    --variable="version:$RELEASE_VERSION" \
-    --output=notes.md \
-    "$notes_body" || die
+    "$notes_body" \
+  | \
+    pandoc --from=gfm --to=gfm \
+      --template=.github/RELEASE_DRAFT_TEMPLATE.md \
+      --shift-heading-level-by=1 --wrap=none \
+      --variable="version:$RELEASE_VERSION" \
+      --output=notes.md || die
   if [ -n "$overwrite" ]
   then
     # Is there an existing release?