Update changelog for v3.21.4 release
## Unreleased
+## 3.21.4 (September 22, 2022)
+
+New tag to fix a publishing error for the Java SDK
+
## 3.21.3 (September 22, 2022)
- Fix Helm Chart preview with unconfigured provider (C#) (https://github.com/pulumi/pulumi-kubernetes/issues/2162)
