Further fix docs deployment workflow. (#82)

(it's only testable after merging to main)

.github/workflows/docs.yml

@@ -54,9 +54,6 @@ jobs:
     if: ${{ needs.deploy-precheck.outputs.gh-deploy-key == 'true' }}
     runs-on: ubuntu-latest
     steps:
-      - name: Check secret set
-        run: |
-          echo "GH_PAGES_DEPLOY: ${{ secrets.GH_PAGES_DEPLOY }}"
       - uses: actions/checkout@v4
         with:
           fetch-depth: 0
@@ -72,7 +69,7 @@ jobs:
           cache: yarn
       - uses: webfactory/ssh-agent@v0.5.0
         with:
-          ssh-private-key: ${{ env.GH_PAGES_DEPLOY }}
+          ssh-private-key: ${{ secrets.GH_PAGES_DEPLOY }}
       - name: Deploy to GitHub Pages
         env:
           USE_SSH: true