Update CHANGELOG with fixes and improvements

Added a section for fixes and improvements in CHANGELOG.

Author: stefanosiano

CHANGELOG.md

@@ -15,6 +15,10 @@
   }
   ```
 
+### Fixes
+
+- Flush logs on crash ([#4684](https://github.com/getsentry/sentry-java/pull/4684))
+
 ### Improvements
 
 - Remove internal API status from get/setDistinctId ([#4708](https://github.com/getsentry/sentry-java/pull/4708))
@@ -47,10 +51,6 @@
 - Add support for `vars` attribute in `SentryStackFrame` ([#4686](https://github.com/getsentry/sentry-java/pull/4686))
   - **Breaking change**: The type of the `vars` attribute has been changed from `Map<String, String>` to `Map<String, Object>`.
 
-### Fixes
-
-- Flush logs on crash ([#4684](https://github.com/getsentry/sentry-java/pull/4684))
-
 ## 8.20.0
 
 ### Fixes