Use Node V20 in Github CI

The CI job has been failing. Use the same version as what the relay repo is using https://github.com/facebook/relay/blob/main/.github/workflows/ci.yml

Author: tyao1

Diff for: .github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
       - uses: actions/checkout@v1
       - uses: actions/setup-node@v1
         with:
-          node-version: 12.x
+          node-version: 20.x
       - name: Install dependencies
         run: yarn install --frozen-lockfile
       - name: Check formatting