use nightly flag

Author: mehul-jain1

.github/workflows/nightly.yml

@@ -13,4 +13,6 @@ jobs:
   Acceptance:
     needs: Spec
     uses: "puppetlabs/cat-github-actions/.github/workflows/module_acceptance.yml@main"
+    with:
+      flags: '--nightly'
     secrets: "inherit"