Update test-docker-build.yml

.github/workflows/test-docker-build.yml

@@ -28,7 +28,8 @@ jobs:
             echo "$file was changed"
           done 
           echo ${{ steps.changed-files.outputs.all_changed_files}}
-          echo "matrix=[\"${{ steps.changed-files.outputs.all_changed_files}}\"] |sed 's/ /\", \"/g'" >> $GITHUB_OUTPUT
+          echo "[\"${{ steps.changed-files.outputs.all_changed_files}}\"] | sed 's/ /\", \"/g'" >> $MATRIX
+          echo "matrix=$MATRIX" >> $GITHUB_OUTPUT
   build_modified_files:
     needs: get_changed_files
     name: Build Docker images on modified files