⬆️ Bump actions/checkout from 3 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v3...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] <support@github.com>

Author: dependabot[bot]

.github/workflows/build-init.yml

@@ -17,7 +17,7 @@ jobs:
       VAGRANT_ON_GH: true
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: set up Python
       uses: actions/setup-python@v5
       with:

.github/workflows/build-vagrant.yml

@@ -23,7 +23,7 @@ jobs:
       VAGRANT_ON_GH: true
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
 
     - name: set up Python
       uses: actions/setup-python@v5

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v6
     - name: Set up Python
       uses: actions/setup-python@v4
       with: