fix(e2e): restore Build plugin step indentation

The RBAC step removal accidentally moved Build plugin to root level.
Fixes YAML parse error that would prevent E2E workflow from running.

.github/workflows/e2e.yaml

@@ -48,7 +48,7 @@ jobs:
       - name: Install dependencies
         run: npm ci
 
-- name: Build plugin
+      - name: Build plugin
         run: npx @kinvolk/headlamp-plugin build
 
       - name: Deploy E2E Headlamp instance
@@ -100,4 +100,4 @@ jobs:
         with:
           name: test-results
           path: test-results/
-          retention-days: 7
+          retention-days: 7