Bump actions/setup-node from 4 to 6 (#3)

Bumps [actions/setup-node](https://github.com/actions/setup-node) from 4 to 6.
- [Release notes](https://github.com/actions/setup-node/releases)
- [Commits](https://github.com/actions/setup-node/compare/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>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/ci.yaml

@@ -34,7 +34,7 @@ jobs:
     steps:
       - uses: actions/checkout@v6
 
-      - uses: actions/setup-node@v4
+      - uses: actions/setup-node@v6
         with:
           node-version: 24
           cache: npm
@@ -70,7 +70,7 @@ jobs:
       - name: Publish .NET API (required for CDK asset path)
         run: dotnet publish api/src/ProposalSystem.Api/ProposalSystem.Api.csproj --configuration Release --runtime linux-arm64 --self-contained
 
-      - uses: actions/setup-node@v4
+      - uses: actions/setup-node@v6
         with:
           node-version: 24
           cache: npm

.github/workflows/deploy.yaml

@@ -16,7 +16,7 @@ jobs:
     steps:
       - uses: actions/checkout@v6
 
-      - uses: actions/setup-node@v4
+      - uses: actions/setup-node@v6
         with:
           node-version: 24
           cache: npm