Chore(deps): 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](https://github.com/actions/checkout/compare/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>

.github/workflows/ci.yml

@@ -37,7 +37,7 @@ jobs:
     env:
       DOCKER_BUILDKIT: "1"
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - uses: reviewdog/action-misspell@v1
         with:
@@ -78,7 +78,7 @@ jobs:
     runs-on: ubuntu-latest
     environment: secrets
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - run: docker build -t qmcgaw/gluetun .
 
@@ -103,7 +103,7 @@ jobs:
       contents: read
       security-events: write
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/setup-go@v6
         with:
           go-version-file: go.mod
@@ -128,7 +128,7 @@ jobs:
       packages: write
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       # extract metadata (tags, labels) for Docker
       # https://github.com/docker/metadata-action

.github/workflows/labels.yml

@@ -11,7 +11,7 @@ jobs:
       issues: write
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: crazy-max/ghaction-github-labeler@v5
         with:
           yaml-file: .github/labels.yml

.github/workflows/markdown.yml

@@ -18,7 +18,7 @@ jobs:
       actions: read
       contents: read
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - uses: DavidAnson/markdownlint-cli2-action@v21
         with: