Fix E2E workflow: use pnpm-capable reusable workflow branch

The reusable plugin-e2e.yaml@main lacks pnpm support. Switching to
the PR branch that has pnpm detector, Corepack setup, and pnpm commands.

Will revert to @main once PR #141 merges.

- PRI-619 E2E fix

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.github/workflows/e2e.yaml

@@ -16,7 +16,7 @@ concurrency:
 
 jobs:
   e2e:
-    uses: privilegedescalation/.github/.github/workflows/plugin-e2e.yaml@main
+    uses: privilegedescalation/.github/.github/workflows/plugin-e2e.yaml@hugh/add-pnpm-support-plugin-e2e
     with:
       node-version: '22'
       headlamp-version: v0.40.1