Bump versions for v0.21.0 release

Signed-off-by: Kate Goldenring <[email protected]>

Author: kate-goldenring

CHANGELOG.md

@@ -4,8 +4,14 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 
 ## [Unreleased]
 
+### Changed
+- 
+
+## [v0.21.0] - 2025-08-27
+
 ### Changed
 - Update to use Spin v3.4.0 dependencies ([#355](https://github.com/spinframework/containerd-shim-spin/pull/355))
+- Add script to easily update project version before releases ([#200](https://github.com/spinframework/containerd-shim-spin/pull/200))
 
 ## [v0.20.0] - 2025-06-25