Add wait for MachineList to be available

Signed-off-by: muhammad adil ghaffar <muhammad.adil.ghaffar@est.tech>

test/e2e/clusterctl_upgrade.go

@@ -548,6 +548,25 @@ func ClusterctlUpgradeSpec(ctx context.Context, inputGetter func() ClusterctlUpg
 				input.PostUpgrade(managementClusterProxy, workloadClusterNamespace, managementClusterName)
 			}
 
+			// After the upgrade check that MachineList is available. This ensures the APIServer is serving without
+			// error before checking that it `Consistently` returns the MachineList later on.
+			Byf("[%d] Waiting for MachineList to be available", i)
+			Eventually(func() error {
+				postUpgradeMachineList := &unstructured.UnstructuredList{}
+				postUpgradeMachineList.SetGroupVersionKind(schema.GroupVersionKind{
+					Group:   clusterv1.GroupVersion.Group,
+					Version: coreCAPIStorageVersion,
+					Kind:    "MachineList",
+				})
+				err = managementClusterProxy.GetClient().List(
+					ctx,
+					postUpgradeMachineList,
+					client.InNamespace(workloadCluster.GetNamespace()),
+					client.MatchingLabels{clusterv1.ClusterNameLabel: workloadCluster.GetName()},
+				)
+				return err
+			}, "3m", "30s").ShouldNot(HaveOccurred(), "MachineList should be available after the upgrade")
+
 			// After the upgrade check that there were no unexpected rollouts.
 			Byf("[%d] Verify there are no unexpected rollouts", i)
 			Consistently(func() bool {