chore: Support Node 18+ (#1980)

* feat: Support Node 18+

* chore: Additional Node 18 upgrades

* chore: don't change test fixtures

* feat: Move kokoro directories to 18

* chore: Update checkout and setup-node to v4

- https://github.com/actions/checkout/releases/tag/v4.0.0

- https://github.com/actions/setup-node/releases/tag/v4.0.0

Source-Link: googleapis/synthtool@c19dd80
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-nodejs:latest@sha256:8060aba1f6d5617d08091767141ab2a99ea1ccbd9371fd42ffc208c5329caa73

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

.github/.OwlBot.lock.yaml

@@ -13,5 +13,5 @@
 # limitations under the License.
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-nodejs:latest
-  digest: sha256:609822e3c09b7a1bd90b99655904609f162cc15acb4704f1edf778284c36f429
-# created: 2024-10-01T19:34:30.797530443Z
+  digest: sha256:8060aba1f6d5617d08091767141ab2a99ea1ccbd9371fd42ffc208c5329caa73
+# created: 2024-10-04T00:09:31.22876583Z

.github/workflows/ci.yaml

@@ -9,10 +9,10 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node: [14, 16, 18, 20]
+        node: [14, 16, 18}]
     steps:
-      - uses: actions/checkout@v3
-      - uses: actions/setup-node@v3
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
         with:
           node-version: ${{ matrix.node }}
       - run: node --version
@@ -29,30 +29,30 @@ jobs:
   windows:
     runs-on: windows-latest
     steps:
-      - uses: actions/checkout@v3
-      - uses: actions/setup-node@v3
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
         with:
-          node-version: 14
+          node-version: 18
       - run: npm install --engine-strict
       - run: npm test
         env:
           MOCHA_THROW_DEPRECATION: false
   lint:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
-      - uses: actions/setup-node@v3
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
         with:
-          node-version: 14
+          node-version: 18
       - run: npm install
       - run: npm run lint
   docs:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
-      - uses: actions/setup-node@v3
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
         with:
-          node-version: 14
+          node-version: 18
       - run: npm install
       - run: npm run docs
       - uses: JustinBeckwith/linkinator-action@v1