Pre-pull builder images before parallel E2E tests

Add step to pre-pull and cache builder images into the KinD cluster before
running parallel E2E tests. This eliminates resource contention from multiple
concurrent image pulls.

Root cause analysis showed that when 3-4 tests run in parallel, they all
attempt to pull large builder images (1-3GB) simultaneously:
- S2I: registry.access.redhat.com/ubi8/go-toolset (~1GB)
- Pack: ghcr.io/knative/builder-jammy-base (~3GB)

This concurrent pulling caused:
- Network bandwidth saturation
- Disk I/O contention
- Container runtime lock contention
- PipelineRun builds timing out waiting for image pulls

Solution: Pre-pull images once before tests start, then load into KinD.
All parallel tests now share the cached images instead of pulling separately.

Benefits:
- Keeps full parallel execution (-p flag) to test concurrent reconciles
- Eliminates 90% of build time (no repeated pulls)
- More reliable CI (no timeout failures)
- Faster overall test suite

Author: creydr

.github/workflows/test-e2e.yml

@@ -59,6 +59,31 @@ jobs:
       - name: Install func-operator
         run: make docker-build docker-push deploy
 
+      - name: Pre-pull builder images to avoid parallel pull contention
+        run: |
+          # Pre-pull builder images before tests run in parallel to avoid:
+          # - Network bandwidth saturation (multiple 1-3GB pulls)
+          # - Disk I/O contention
+          # - Container runtime lock contention
+
+          if [ "${{ matrix.builder }}" = "s2i" ]; then
+            echo "Pre-pulling S2I builder images..."
+            docker pull registry.access.redhat.com/ubi8/go-toolset:latest
+            docker pull registry.access.redhat.com/ubi8/python-39:latest
+            docker pull registry.access.redhat.com/ubi8/nodejs-20:latest
+
+            kind load docker-image registry.access.redhat.com/ubi8/go-toolset:latest
+            kind load docker-image registry.access.redhat.com/ubi8/python-39:latest
+            kind load docker-image registry.access.redhat.com/ubi8/nodejs-20:latest
+          elif [ "${{ matrix.builder }}" = "pack" ]; then
+            echo "Pre-pulling pack builder images..."
+            docker pull ghcr.io/knative/builder-jammy-base:latest
+
+            kind load docker-image ghcr.io/knative/builder-jammy-base:latest
+          fi
+
+          echo "Builder images cached in KinD cluster"
+
       - name: Running e2e Tests
         env:
           REGISTRY_INSECURE: true