chore: update dependabot config

[skip ci]

Signed-off-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

.github/dependabot.yml

@@ -90,3 +90,14 @@ updates:
       github-actions-dependencies:
         patterns:
           - '*'
+  - package-ecosystem: github-actions
+    directory: /actions/helm/test-chart
+    open-pull-requests-limit: 20
+    schedule:
+      interval: weekly
+      day: friday
+      time: '04:00'
+    groups:
+      github-actions-dependencies:
+        patterns:
+          - '*'