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] <support@github.com>

Author: dependabot[bot]

.github/workflows/CI.yml

@@ -9,7 +9,7 @@ jobs:
   Cinnamon:
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Free up disk space for the CI
         uses: AdityaGarg8/remove-unwanted-software@v5
@@ -74,7 +74,7 @@ jobs:
   Mate:
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Free up disk space for the CI
         uses: AdityaGarg8/remove-unwanted-software@v5
@@ -134,7 +134,7 @@ jobs:
   XFCE:
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Free up disk space for the CI
         uses: AdityaGarg8/remove-unwanted-software@v5
@@ -197,7 +197,7 @@ jobs:
     steps:
 
       - name: 'Checkout Repo'
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Generate Variables
         run: |