Update CHANGELOG.md

Author: jpnurmi

CHANGELOG.md

@@ -6,6 +6,9 @@
 
 - Provide `before_send_transaction` callback. ([#1236](https://github.com/getsentry/sentry-native/pull/1236))
 
+**Fixes**:
+- Close file and return 0 on success when writing raw envelopes. ([#1260](https://github.com/getsentry/sentry-native/pull/1260))
+
 **Docs**:
 
 - Document convenience Powershell runners for formatting and tests on Windows. ([#1247](https://github.com/getsentry/sentry-native/pull/1247))