Optional tests failing: Flatcar and RKE tests don't have artifacts for k8s v1.33.10

[willie-yao]

Which jobs are failing:
pull-cluster-api-provider-azure-e2e-optional

Which tests are failing:
Creating a Flatcar sysext cluster [OPTIONAL] With Flatcar control-plane and worker nodes
Creating RKE2 clusters using clusterclass [OPTIONAL] with 3 control plane node and one linux worker node

Since when has it been failing:
Since v1.33.10 release

Testgrid link:
https://prow.k8s.io/view/gs/kubernetes-ci-logs/pr-logs/pull/kubernetes-sigs_cluster-api-provider-azure/6165/pull-cluster-api-provider-azure-e2e-optional/2036211398081515520

Reason for failure (if possible):
Flatcar and RKE2 have not published artifacts for v1.33.10

Anything else we need to know:

/kind failing-test

[One or more /area label. See https://github.com/kubernetes-sigs/cluster-api/labels?q=area for the list of labels]

[willie-yao]

Temporarily pinning optional tests to v1.33.9 to fix CI: kubernetes/test-infra#36728

[mboersma]

Both Flatcar and RKE2 now have published v1.33.10 artifacts, according to CoPilot:

Artifact	v1.33.10 available?	Verified
Flatcar sysext (kubernetes-v1.33.10-x86-64.raw)	Yes — exists at extensions.flatcar.org	Download URL confirmed
RKE2 release (v1.33.10+rke2r3)	Yes — released last week	rancher/rke2 releases
stable-1.33 Kubernetes version	Resolves to v1.33.10	Confirmed via dl.k8s.io

[willie-yao]

@mboersma Okay I'll revert the test-infra PR!

[willie-yao]

kubernetes/test-infra#36818