[Bug] create cluster fails when VPC CNI is configured to use both `iam.withOIDC` and `useDefaultPodIdentityAssociations`

[guessi]

What were you trying to accomplish?

Trying to get #7925 issue fixed.

What happened?

panic if set both iam.withOIDC and useDefaultPodIdentityAssociations at the same time.

How to reproduce it?

Create cluster with minimal ClusterConfig as follow

apiVersion: eksctl.io/v1alpha5
kind: ClusterConfig

metadata:
  name: cluster-debug

iam:
  withOIDC: true

addons:
  - name: kube-proxy
    version: latest
  - name: vpc-cni
    version: latest
    useDefaultPodIdentityAssociations: true
  - name: coredns
    version: latest
  - name: eks-pod-identity-agent
    version: latest

Logs

$ eksctl create cluster -f cluster-config.yaml
2025-01-14 14:40:39 [ℹ]  eksctl version 0.200.0
...
2025-01-14 14:53:10 [ℹ]  creating addon
2025-01-14 14:53:10 [ℹ]  successfully created addon
2025-01-14 14:53:11 [ℹ]  creating addon
2025-01-14 14:53:12 [ℹ]  successfully created addon
2025-01-14 14:53:12 [ℹ]  "addonsConfig.autoApplyPodIdentityAssociations" is set to true; will lookup recommended pod identity configuration for "vpc-cni" addon
2025-01-14 14:53:14 [ℹ]  deploying stack "eksctl-eks-demo-full-addon-vpc-cni-podidentityrole-aws-node"
2025-01-14 14:53:14 [ℹ]  waiting for CloudFormation stack "eksctl-eks-demo-full-addon-vpc-cni-podidentityrole-aws-node"
2025-01-14 14:53:45 [ℹ]  waiting for CloudFormation stack "eksctl-eks-demo-full-addon-vpc-cni-podidentityrole-aws-node"
2025-01-14 14:53:45 [ℹ]  creating addon
2025-01-14 14:53:46 [ℹ]  successfully created addon
2025-01-14 14:53:47 [ℹ]  creating addon
2025-01-14 14:53:47 [ℹ]  successfully created addon
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0x20 pc=0x103c20b78]

goroutine 214 [running]:
github.com/weaveworks/eksctl/pkg/actions/addon.(*Manager).Update(0x140002aca00, {0x10633d128, 0x108b2f8a0}, 0x14000286d20, {0x0, 0x0}, 0x15d3ef79800)
	github.com/weaveworks/eksctl/pkg/actions/addon/update.go:121 +0xeb8
github.com/weaveworks/eksctl/pkg/actions/addon.CreateAddonTasks.func3()
	github.com/weaveworks/eksctl/pkg/actions/addon/tasks.go:93 +0x90
github.com/weaveworks/eksctl/pkg/utils/tasks.(*GenericTask).Do(0x140009c9290, 0x0?)
	github.com/weaveworks/eksctl/pkg/utils/tasks/tasks.go:31 +0x34
github.com/weaveworks/eksctl/pkg/utils/tasks.doSingleTask(0x0?, {0x1062ea5b8, 0x140009c9290})
	github.com/weaveworks/eksctl/pkg/utils/tasks/tasks.go:202 +0xc8
github.com/weaveworks/eksctl/pkg/utils/tasks.doSequentialTasks(0x0?, {0x1400057b400, 0x5, 0x140007740b0?})
	github.com/weaveworks/eksctl/pkg/utils/tasks/tasks.go:250 +0x6c
created by github.com/weaveworks/eksctl/pkg/utils/tasks.(*TaskTree).Do in goroutine 212
	github.com/weaveworks/eksctl/pkg/utils/tasks/tasks.go:158 +0x258

Anything else we need to know?

Versions

$ eksctl info
eksctl version: 0.200.0
kubectl version: v1.32.0
OS: darwin