ci(actions): 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

@@ -19,7 +19,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v6
-      - uses: actions/setup-node@v4
+      - uses: actions/setup-node@v6
         with:
           node-version: "24"
       - uses: pnpm/action-setup@v5
@@ -39,7 +39,7 @@ jobs:
     needs: quality
     steps:
       - uses: actions/checkout@v6
-      - uses: actions/setup-node@v4
+      - uses: actions/setup-node@v6
         with:
           node-version: "24"
       - uses: pnpm/action-setup@v5
@@ -81,7 +81,7 @@ jobs:
         with:
           fetch-depth: 0
           persist-credentials: false
-      - uses: actions/setup-node@v4
+      - uses: actions/setup-node@v6
         with:
           node-version: "24"
           # Do NOT set registry-url — it creates an .npmrc that overrides OIDC