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

@@ -15,11 +15,11 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Set up Go
         uses: actions/setup-go@v6
         with:
-          go-version: "1.25.5"
+          go-version: "1.25.4"
       - name: Cache Go modules
         uses: actions/cache@v4
         with:
@@ -47,11 +47,11 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Set up Go
         uses: actions/setup-go@v6
         with:
-          go-version: "1.25.5"
+          go-version: "1.25.4"
       - name: Run golangci-lint
         uses: golangci/golangci-lint-action@v8
         with: