ci: Update Node.js version to 16

Updates to use the latest (3.6.0) release of
[setup-node](https://github.com/actions/setup-node) and bumps the
Node.js version to 16.

This should also get rid of deprecation warnings we're seeing in our
workflow actions (for example,
https://github.com/tensorflow/tensorboard/actions/runs/3388287772).

Resolves tensorflow#6123.

.github/workflows/ci.yml

@@ -308,10 +308,9 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@50fbc622fc4ef5163becd7fab6573eac35f8462e
-      - uses: actions/setup-node@56899e050abffc08c2b3b61f3ec6a79a9dc3223d
+      - uses: actions/setup-node@64ed1c7eab4cce3362f8c340dee64e5eaeef8f7c # v3.6.0
         with:
-          # default on setup-node@1 is v10.24.1.
-          node-version: '12.21.0'
+          node-version: 16
       - run: yarn install --ignore-engines
         # You can run `yarn fix-lint` to fix all Prettier complaints.
       - run: yarn lint