Fix chart linting (kubernetes#1612)

Author: brtkwr

.github/workflows/pr.yaml

@@ -12,8 +12,17 @@ jobs:
       - name: Fetch history
         run: git fetch --prune --unshallow
 
-      - id: lint
-        name: Run chart-testing (lint)
-        uses: helm/[email protected]
+      - name: Set up Helm
+        uses: azure/setup-helm@v1
         with:
-          command: lint
+          version: v3.6.1
+
+      - uses: actions/setup-python@v2
+        with:
+          python-version: 3.7
+
+      - name: Set up chart-testing
+        uses: helm/[email protected]
+
+      - name: Run chart-testing (lint)
+        run: ct lint --target-branch ${GITHUB_BASE_REF}