replace set-output usage (#1)

README.md

@@ -35,9 +35,9 @@ The action returns either `true` or `false`, indicating if the derived image dif
 
 ```yaml
 - name: Run
-id: run
-uses: ClementTsang/docker-check-base-image-diff@v0.0.1-alpha
-with:
+  id: run
+  uses: ClementTsang/docker-check-base-image-diff@v0.0.1-alpha
+  with:
     base-image: docker://rust:slim-buster
     derived-image: docker://ghcr.io/clementtsang/cargo-deb-arm
 ```

action.yml

@@ -24,4 +24,4 @@ runs:
       shell: bash
       run: |
         RESULT=$(${{ github.action_path }}/check.sh ${{ inputs.base-image }} ${{ inputs.derived-image }})
-        echo "::set-output name=differs::$RESULT"
+        echo "differs=$RESULT" >> $GITHUB_OUTPUT