Update dependency cert-manager/cert-manager to v1.18.1 (#588)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

hack/config/cert-manager/kustomization.yaml

@@ -2,7 +2,7 @@ apiVersion: kustomize.config.k8s.io/v1beta1
 kind: Kustomization
 
 resources:
-- https://github.com/cert-manager/cert-manager/releases/download/v1.18.0/cert-manager.yaml
+- https://github.com/cert-manager/cert-manager/releases/download/v1.18.1/cert-manager.yaml
 
 patches:
 # lower the webhook timeouts to make the webhooks compliant with gardener's requirements