ci: Use GITHUB_OUTPUT envvar instead of set-output command

`save-state` and `set-output` commands used in GitHub Actions are deprecated and [GitHub recommends using environment files](https://github.blog/changelog/2023-07-24-github-actions-update-on-save-state-and-set-output-commands/).

This PR updates the usage of `::set-output` to `"$GITHUB_OUTPUT"`

Instructions for envvar usage from GitHub docs:

https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#setting-an-output-parameter

.github/workflows/test.yml

@@ -16,7 +16,7 @@ jobs:
       - name: Get npm cache directory
         id: npm-cache
         run: |
-          echo "::set-output name=dir::$(npm config get cache)"
+          echo "dir=$(npm config get cache)" >> "$GITHUB_OUTPUT"
       - uses: actions/cache@v4
         with:
           path: ${{ steps.npm-cache.outputs.dir }}