feat!: Support Node 18+ (#2011)

* 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

Author: d-goog

synthtool/gcp/templates/node_library/.github/workflows/ci.yaml

@@ -9,10 +9,10 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node: [{{metadata['engine'] | int}}, {{metadata['engine'] | int+2}}, {{metadata['engine'] | int+4}}, {{metadata['engine'] | int+6}}]
+        node: [{{metadata['engine'] | int}}, {{metadata['engine'] | int+2}}, {{metadata['engine'] | int+4}}}]
     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