fix issue 3945

[vaikas]

Fixes #3945

Proposed Changes

• Check the length of the branches and if they change, realloc the array of BranchStatuses. Otherwise, if branches are added, panic happens.

Release Note

- 🐛 Fix bug
If you create a Parallel, then later add branches to it, caused a panic.

Docs

[knative-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: vaikas

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• OWNERS [vaikas]

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[lionelvillard]

/lgtm

[knative-test-reporter-robot]

The following jobs failed:

Test name	Triggers	Retries
pull-knative-eventing-integration-tests		0/3

Failed non-flaky tests preventing automatic retry of pull-knative-eventing-integration-tests:

test/e2e.TestSingleBinaryEventForChannelV1Beta1/InMemoryChannel-messaging.knative.dev/v1beta1
test/e2e.TestSingleBinaryEventForChannelV1Beta1

[vaikas]

Failed with:

=== CONT  TestSingleBinaryEventForChannelV1Beta1/InMemoryChannel-messaging.knative.dev/v1beta1
    creation.go:153: Failed to create subscription "e2e-singleevent-subscription-binary": conversion webhook for messaging.knative.dev/v1, Kind=Subscription failed: Post https://eventing-webhook.knative-eventing-8eex0grbyp.svc:443/resource-conversion?timeout=30s: EOF
    creation.go:148: Creating v1beta1 subscription e2e-singleevent-subscription-binary for channel &TypeMeta{Kind:InMemoryChannel,APIVersion:messaging.knative.dev/v1beta1,}-e2e-singleevent-channel-binary
    creation.go:153: Failed to create subscription "e2e-singleevent-subscription-binary": subscriptions.messaging.knative.dev "e2e-singleevent-subscription-binary" already exists
    tracker.go:152: Waiting for all KResources to become ready
Failed to get /: name is required    operation.go:94: Failed to get all KResources ready failed waiting for {TypeMeta:{Kind:Subscription APIVersion:messaging.knative.dev/v1beta1} ObjectMeta:{Name: GenerateName: Namespace: SelfLink: UID: ResourceVersion: Generation:0 CreationTimestamp:0001-01-01 00:00:00 +0000 UTC DeletionTimestamp:<nil> DeletionGracePeriodSeconds:<nil> Labels:map[] Annotations:map[] OwnerReferences:[] Finalizers:[] ClusterName: ManagedFields:[]}} to become ready: name is required
    operation.go:115: Failed to get all test resources ready: failed waiting for {TypeMeta:{Kind:Subscription APIVersion:messaging.knative.dev/v1beta1} ObjectMeta:{Name: GenerateName: Namespace: SelfLink: UID: ResourceVersion: Generation:0 CreationTimestamp:0001-01-01 00:00:00 +0000 UTC DeletionTimestamp:<nil> DeletionGracePeriodSeconds:<nil> Labels:map[] Annotations:map[] OwnerReferences:[] Finalizers:[] ClusterName: ManagedFields:[]}} to become ready: name is required
        knative.dev/eventing/test/lib.(*Client).WaitForAllTestResourcesReadyOrFail
        	/home/prow/go/src/knative.dev/eventing/test/lib/operation.go:115
        knative.dev/eventing/test/e2e/helpers.SingleEventForChannelTestHelper.func1
        	/home/prow/go/src/knative.dev/eventing/test/e2e/helpers/channel_single_event_helper.go:94
        knative.dev/eventing/test/lib.(*ComponentsTestRunner).RunTests.func1
        	/home/prow/go/src/knative.dev/eventing/test/lib/test_runner.go:72
        testing.tRunner
        	/root/.gvm/gos/go1.14.6/src/testing/testing.go:1039
        runtime.goexit
        	/root/.gvm/gos/go1.14.6/src/runtime/asm_amd64.s:1373

Created #3949 to track that issue.

/test pull-knative-eventing-integration-tests