ci(node): use Node 16 for testing on CI

reduce the duration of CI tests whose log prints out that several modules don't support Node 15 but Node 16.

.github/workflows/validate.yml

@@ -9,7 +9,7 @@ jobs:
       - name: 'Install Node'
         uses: actions/setup-node@v2
         with:
-          node-version: '15'
+          node-version: '16'
           cache: 'npm'
       - name: 'Install repo'
         run: npm install