chore(deps): update helm/chart-testing-action action to v2.8.0

Author: renovate[bot]

.github/workflows/helm.yaml

@@ -30,7 +30,7 @@ jobs:
           python-version: 3.7
 
       - name: Set up chart-testing
-        uses: helm/chart-testing-action@v2.6.1
+        uses: helm/chart-testing-action@v2.8.0
 
       - name: Run chart-testing (list-changed)
         id: list-changed