Prepare for 4.18.3 release (#3296)

### Fixed

- Objects created on clusters older than 1.18 will no longer see a
`before-first-apply` conflict when Pulumi performs a server-side apply
for the first time.
(#3275)

- The provider's user agent is now set correctly when communicating with
the Kubernetes API server.
(#3267)

CHANGELOG.md

@@ -1,5 +1,7 @@
 ## Unreleased
 
+## 4.18.3 (October 31, 2024)
+
 ### Fixed
 
 - Objects created on clusters older than 1.18 will no longer see a