build!: update library to use Node 12 (#589)

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md
Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: alexander-fenster

.github/sync-repo-settings.yaml

@@ -9,9 +9,9 @@ branchProtectionRules:
       - "ci/kokoro: System test"
       - docs
       - lint
-      - test (10)
       - test (12)
       - test (14)
+      - test (16)
       - cla/google
       - windows
       - OwlBot Post Processor

.github/workflows/ci.yaml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node: [10, 12, 14]
+        node: [12, 14, 16]
     steps:
       - uses: actions/checkout@v3
       - uses: actions/setup-node@v3