Update helm/chart-testing-action action to v2.8.0

Author: renovate[bot]

.github/workflows/main.yaml

@@ -28,7 +28,7 @@ jobs:
           check-latest: true
 
       - 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