Bump actions/checkout from 5 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...v6)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/melinda-node-tests-and-publish.yml

@@ -20,7 +20,7 @@ jobs:
 
     steps:
     - name: Checkout the code
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     - name: Use Node.js ${{ matrix.node-version }}
       uses: actions/setup-node@v6
       with:
@@ -39,7 +39,7 @@ jobs:
     container: node:22
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: mikaelvesavuori/license-compliance-action@v1
         with:
           exclude_pattern: /^@natlibfi/
@@ -51,7 +51,7 @@ jobs:
 
     steps:
     - name: Checkout the code
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     - name: nodejsscan scan
       id: njsscan
       uses: ajinabraham/njsscan-action@master
@@ -65,7 +65,7 @@ jobs:
     if: contains(github.ref, 'refs/tags/')
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       # Setup .npmrc file to publish to npm
       - name: Prepare node for publish
         uses: actions/setup-node@v6