ci: update helm linter to v2.6.0

The helm linter was failing with v2.4.0. Now
update the version of the action to the latest
and greatest.

Signed-off-by: travisn <tnielsen@redhat.com>
(cherry picked from commit dfa522d906)

.github/workflows/helm-lint.yaml

@@ -40,7 +40,7 @@ jobs:
           python-version: 3.9
 
       - name: Set up chart-testing
-        uses: helm/chart-testing-action@v2.4.0
+        uses: helm/chart-testing-action@v2.6.0
 
       - name: Run chart-testing (lint)
         run: ct lint --charts=./deploy/charts/rook-ceph --validate-yaml=false --validate-maintainers=false