[CI] Try fixing tangle roots with subfolders

Author: eliemichel

.github/workflows/tangle.yml

@@ -52,7 +52,7 @@ jobs:
 
     - name: List tangle roots
       id: set-tangle-roots
-      run: echo "roots=${{fromJson(steps.read-tangle-metadata.outputs.metadata).roots}}" >> $GITHUB_OUTPUT
+      run: echo "roots=${{toJson(fromJson(steps.read-tangle-metadata.outputs.metadata).roots)}}" >> $GITHUB_OUTPUT
 
     - name: Upload artifact
       uses: actions/upload-artifact@v4