docs: replace set-output with GITHUB_OUTPUT

close #633

README.md

@@ -185,7 +185,7 @@ Next, add a step to read a Hugo version from the `.env` file.
       id: hugo-version
       run: |
         . ./.env
-        echo "::set-output name=HUGO_VERSION::${HUGO_VERSION}"
+        echo "HUGO_VERSION=${HUGO_VERSION}" >> "${GITHUB_OUTPUT}"
 
     - name: Setup Hugo
       uses: peaceiris/actions-hugo@v2