fix(chart-lint): make the lint and changed tests branch-aware

Author: drcgjung

.github/workflows/helm-chart-lint.yml

@@ -76,11 +76,11 @@ jobs:
       - name: Run chart-testing (list-changed)
         id: list-changed
         run: |
-          changed=$(ct list-changed --target-branch ${{ github.event.ref }})
+          changed=$(ct list-changed --target-branch ${{ github.base_ref || github.ref_name }})
           if [[ -n "$changed" ]]; then
             echo "CHART_CHANGED=true" >> $GITHUB_ENV
           fi
 
       # run chart linting
       - name: Run chart-testing (lint)
-        run: ct lint --target-branch ${{ github.event.ref }} --config charts/config/chart-testing-config.yaml
+        run: ct lint --target-branch ${{ github.base_ref || github.ref_name }} --config charts/config/chart-testing-config.yaml