Fix tc-lint glob handling for charts without ci/*values.yaml (#45013)

Lint runs were emitting `ls: cannot access '.../ci/*values.yaml'` for
charts that do not define CI override files (e.g.
`charts/stable/friendica`). The issue came from using `ls` as a glob
existence check in `tc-lint.sh`.

- **Root cause**
- `helm_lint()` used `ls $chart_path/ci/*values.yaml` inside a
conditional; when the glob had no matches, `ls` printed an error.

- **Change**
- Replaced the `ls`-based check with a silent glob match check using
`compgen -G`.
- Scope is limited to `.github/scripts/tc-lint.sh` and preserves
existing lint decision logic.

- **Behavioral impact**
- Charts without `ci/*values.yaml` no longer produce noisy shell errors
during lint.
  - Existing lint pass/fail behavior remains unchanged.

```bash
# before
if [[ ! $(ls $chart_path/ci/*values.yaml) ]]; then

# after
if ! compgen -G "$chart_path/ci/*values.yaml" >/dev/null; then
```

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.github/scripts/tc-lint.sh

@@ -75,7 +75,7 @@ function helm_lint() {
 
     # TODO: If there are ci/*values.yaml files, lint those
     # and skip linting the top-level values.yaml.
-    if [[ ! $(ls $chart_path/ci/*values.yaml) ]]; then
+    if ! compgen -G "$chart_path/ci/*values.yaml" >/dev/null; then
         if echo "$helm_lint_output" | grep -q "Fail:"; then
             helm_lint_exit_code=1
         fi