CI: Configure yarn cache path using ENV vars

The old syntax was deprecated a while ago.
https://github.blog/changelog/2022-10-10-github-actions-deprecating-save-state-and-set-output-commands/

Author: olleolleolle

.github/workflows/ci.yml

@@ -24,7 +24,7 @@ jobs:
 
       - name: Get yarn cache directory path
         id: yarn-cache-dir-path
-        run: echo "::set-output name=dir::$(yarn cache dir)"
+        run: echo "dir='$(yarn cache dir)'" >> "$GITHUB_OUTPUT"
 
       - uses: actions/cache@v4
         id: yarn-cache # use this to check for `cache-hit` (`steps.yarn-cache.outputs.cache-hit != 'true'`)