Bump actions/checkout from 4 to 6 in the actions group (#2192)

Bumps the actions group with 1 update: [actions/checkout](https://github.com/actions/checkout).


Updates `actions/checkout` from 4 to 6
- [Release notes](https://github.com/actions/checkout/releases)
- [Commits](actions/checkout@v4...v6)

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/citation-check.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-24.04
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0
 

.github/workflows/pr-scope-check.yml

@@ -17,7 +17,7 @@ jobs:
       MAX_NET_ADDITIONS: 1500
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0