Bump actions/checkout from 5 to 6 in the all group

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


Updates `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
  dependency-group: all
...

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

Author: dependabot[bot]

.github/workflows/license-check.yml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout Gobra
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Check license headers
         uses: viperproject/check-license-header@v2
         with:

.github/workflows/test.yml

@@ -33,7 +33,7 @@ jobs:
       FAILURE_LEVEL: "error"
     steps:
       - name: Checkout Gobra
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           submodules: 'recursive'
       - name: Check that Silicon, Carbon, and SIF Plugin reference same silver commit

.github/workflows/update-submodules.yml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out the repo
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           submodules: true