revert outdated set-output

Hmm, the new format as documented doesn't work.
Let's fix this by updating the setup-node action which has builtin cache handling for yarn now as well

Author: fredvd

.github/workflows/build_deploy.yml

@@ -41,7 +41,7 @@ jobs:
       - name: Get yarn cache directory path
         id: yarn-cache-dir-path
         working-directory: submodules/volto
-        run: echo "{dir}={$(yarn cache dir)}" >> $GITHUB_OUTPUT
+        run: echo "::set-output name=dir::$(yarn cache dir)"
       - uses: actions/cache@v1
         id: yarn-cache # use this to check for `cache-hit` (`steps.yarn-cache.outputs.cache-hit != 'true'`)
         with: