CI: Bump actions/checkout from 4 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v4...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/linter.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Clone Repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0
 

.github/workflows/pr_labels.yml

@@ -13,7 +13,7 @@ jobs:
 
     steps:
       - name: Clone repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           # pull_request_target is run under forks, use main repo source
           fetch-depth: 0

.github/workflows/stable-compilation.yml

@@ -61,10 +61,10 @@ jobs:
             libdrm-dev libgbm-dev # only needed for sdl2 on debian 11
 
       - name: Clone Repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         if: github.event.inputs.git-ref == ''
       - name: Clone Repository (with custom ref)
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         if: github.event.inputs.git-ref != ''
         with:
           ref: ${{ github.event.inputs.git-ref }}