Update changelog for v3.20.5 release
## Unreleased
+## 3.20.5 (August 16, 2022)
+
- Update autonaming to use NewUniqueName for deterministic update plans. (https://github.com/pulumi/pulumi-kubernetes/pull/2137)
- Another fix for managed-by label in SSA mode. (https://github.com/pulumi/pulumi-kubernetes/pull/2140)
