ci: always set skip output of optimize-ci workflow (#2593) (#2596)

Co-authored-by: Sion Kang <siontama@gmail.com>

.github/workflows/ci.yml

@@ -26,14 +26,22 @@ jobs:
       contents: read
       pull-requests: write
     outputs:
-      skip: ${{ steps.check_skip.outputs.skip }}
+      skip: ${{ steps.check_skip.outputs.SKIP }}
     steps:
       - name: Optimize CI
         if: ${{ github.event_name == 'pull_request' }}
-        id: check_skip
+        id: graphite-ci-action
         uses: withgraphite/graphite-ci-action@main
         with:
           graphite_token: ${{ secrets.GRAPHITE_CI_OPTIMIZER_TOKEN }}
+      - name: Check if should skip the CI
+        id: check_skip
+        run: |
+          if [ "${{ steps.graphite-ci-action.outputs.skip }}" == "true" ]; then
+            echo "SKIP=true" >> $GITHUB_OUTPUT
+          else
+            echo "SKIP=false" >> $GITHUB_OUTPUT
+          fi
       - name: labeler
         if: github.event.action == 'opened' || github.event.action == 'reopened' || github.event.action == 'syncrhonize'
         uses: lablup/auto-labeler@main # actions/labeler, lablup/size-label-action, lablup/auto-label-in-issue