ci: bump actions/setup-node from 3 to 4

Bumps [actions/setup-node](https://github.com/actions/setup-node) from 3 to 4.
- [Release notes](https://github.com/actions/setup-node/releases)
- [Commits](actions/setup-node@v3...v4)

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

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

.github/workflows/ci.yml

@@ -9,7 +9,7 @@ jobs:
         node: ['16', '18', '19', '20']
     steps:
       - uses: actions/checkout@v4
-      - uses: actions/setup-node@v3
+      - uses: actions/setup-node@v4
         with:
           node-version: ${{ matrix.node }}
       - run: npm ci --omit=dev
@@ -26,7 +26,7 @@ jobs:
           - en_GB.UTF-8
     steps:
       - uses: actions/checkout@v4
-      - uses: actions/setup-node@v3
+      - uses: actions/setup-node@v4
       - run: npm ci
       - run: npm run test:unit
         env: