ci: Use GITHUB_OUTPUT envvar instead of set-output command (#108)

Summary:
`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

Pull Request resolved: #108

Differential Revision: D52891468

Pulled By: JacksonGL

fbshipit-source-id: e1eebcba4d0826774ea02251a2cbef35d98537f3

.github/workflows/gh-pages.yml

@@ -12,11 +12,11 @@ jobs:
       - name: Setup Node
         uses: actions/setup-node@v3
         with:
-          node-version: '16'
+          node-version: "16"
 
       - name: Get yarn cache
         id: yarn-cache
-        run: echo "::set-output name=dir::$(yarn cache dir)"
+        run: echo "dir=$(yarn cache dir)" >> "$GITHUB_OUTPUT"
 
       - name: Cache dependencies
         uses: actions/cache@v2
@@ -30,7 +30,7 @@ jobs:
         run: |
           yarn install
           yarn build
-        working-directory: '.'
+        working-directory: "."
 
       - name: Build website
         run: |