ci: change how env is set

.github/workflows/build.yml

@@ -31,13 +31,13 @@ jobs:
 
       - if: github.ref == 'refs/heads/main'
         name: Conditional(Set tag as `latest`)
-        run: echo ::set-output name=tag::latest
+        run: echo "tag=latest >> $GITHUB_ENV"
 
       - if: startsWith(github.ref, 'refs/tags/')
         name: Conditional(Set tag as `{version}`)
-        run: echo ::set-output name=tag::${GITHUB_REF#refs/*/}
+        run: echo "tag=${GITHUB_REF#refs/*/} >> $GITHUB_ENV"
 
-      - 
+      -
         name: Build and push
         uses: docker/build-push-action@v2
         with: