build(deps): bump helm/chart-testing-action from 2.7.0 to 2.8.0

Bumps [helm/chart-testing-action](https://github.com/helm/chart-testing-action) from 2.7.0 to 2.8.0.
- [Release notes](https://github.com/helm/chart-testing-action/releases)
- [Commits](helm/chart-testing-action@v2.7.0...v2.8.0)

---
updated-dependencies:
- dependency-name: helm/chart-testing-action
  dependency-version: 2.8.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/publish.yaml

@@ -69,7 +69,7 @@ jobs:
         with:
           python-version: 3.13
       - name: Set up chart-testing
-        uses: helm/chart-testing-action@v2.7.0
+        uses: helm/chart-testing-action@v2.8.0
       - uses: actions/setup-go@v6
         with:
           go-version: "1.24"