chore(release/candidate): release 2.4.0 (#6325)

Co-authored-by: adk-bot <223368873+adk-bot@users.noreply.github.com>
Co-authored-by: Yifan <wanyif@google.com>

Author: adk-bot

.github/.release-please-manifest.json

@@ -1,3 +1,3 @@
 {
-  ".": "2.3.0"
+  ".": "2.4.0"
 }