add v.18.5 changelog

Author: nawazkh

CHANGELOG/v1.18.5.md

@@ -0,0 +1,19 @@
+## Changes by Kind
+
+### Bug or Regression
+- fix AzCluster_default and AzCluster_validation webhooks ([#5616](https://github.com/kubernetes-sigs/cluster-api-provider-azure/pull/5616), [@nawazkh](https://github.com/nawazkh))
+
+## Dependencies
+
+### Added
+_Nothing has changed._
+
+### Changed
+- Bump Cert-manager to v1.17.2 ([#5624](https://github.com/kubernetes-sigs/cluster-api-provider-azure/pull/5624), [@mboersma](https://github.com/mboersma))
+
+### Removed
+_Nothing has changed._
+
+## Details
+<!-- markdown-link-check-disable-next-line -->
+https://github.com/kubernetes-sigs/cluster-api-provider-azure/compare/v1.18.4...v1.18.5