ci: bump actions/setup-node from 4 to 6

Bumps [actions/setup-node](https://github.com/actions/setup-node) from 4 to 6.
- [Release notes](https://github.com/actions/setup-node/releases)
- [Commits](actions/setup-node@v4...v6)

---
updated-dependencies:
- dependency-name: actions/setup-node
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -16,7 +16,7 @@ jobs:
         node: [18, 20, 22]
     steps:
       - uses: actions/checkout@v6
-      - uses: actions/setup-node@v4
+      - uses: actions/setup-node@v6
         with:
           node-version: ${{ matrix.node }}
           cache: npm

.github/workflows/docs.yml

@@ -18,7 +18,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v6
-      - uses: actions/setup-node@v4
+      - uses: actions/setup-node@v6
         with: { node-version: '20', cache: 'npm' }
       - run: npm ci
       - run: npm run docs

.github/workflows/release.yml

@@ -14,7 +14,7 @@ jobs:
       id-token: write
     steps:
       - uses: actions/checkout@v6
-      - uses: actions/setup-node@v4
+      - uses: actions/setup-node@v6
         with:
           node-version: 20
           cache: npm

.github/workflows/spec-drift.yml

@@ -15,7 +15,7 @@ jobs:
       issues: write
     steps:
       - uses: actions/checkout@v6
-      - uses: actions/setup-node@v4
+      - uses: actions/setup-node@v6
         with:
           node-version: 20
           cache: npm