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

.github/workflows/release.yml

@@ -24,7 +24,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Checkout
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
     - run: git fetch --tags
     - name: Setup Go
       uses: actions/setup-go@v6

cmd/kubens/fzf.go

@@ -46,6 +46,14 @@ func (op InteractiveSwitchOp) Run(_, stderr io.Writer) error {
 		return fmt.Errorf("kubeconfig error: %w", err)
 	}
 
+	ctxNames, err := kc.ContextNames()
+	if err != nil {
+		return fmt.Errorf("failed to get context names: %w", err)
+	}
+	if len(ctxNames) == 0 {
+		return errors.New("no contexts found in the kubeconfig file")
+	}
+
 	cmd := exec.Command("fzf", "--ansi", "--no-preview")
 	var out bytes.Buffer
 	cmd.Stdin = os.Stdin