fix(preprod): Mention build upload is non-experimental in CHANGELOG

Author: chromy

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+### New Features
+
+- Promote `sentry-cli build upload` command to non-experimental ([#2899](https://github.com/getsentry/sentry-cli/pull/2899)).
+
 ### Deprecations
 
 - Deprecated the `upload-proguard` subcommand's `--platform` flag ([#2863](https://github.com/getsentry/sentry-cli/pull/2863)). This flag appears to have been a no-op for some time, so we will remove it in the next major.