meta: fix changelog (#3252)

Release 3.3.4 was only partially released (it shows in GitHub releases,
but I am not sure to where else it was successfully released). As a
result, the changelog was not updated after the release.

This change splits off the changlog material included in the partial
[3.3.4
release](https://github.com/getsentry/sentry-cli/releases/tag/3.3.4).

Author: szokeasaurusrex

CHANGELOG.md

@@ -10,6 +10,8 @@
 
 - (sourcemaps) Skip non-base64 embedded sourcemaps during injection ([#3243](https://github.com/getsentry/sentry-cli/pull/3243))
 
+## 3.3.4
+
 ### New Features ✨
 
 - Add `sentry-cli build download` command to download installable builds (IPA/APK) by build ID ([#3221](https://github.com/getsentry/sentry-cli/pull/3221)).