Add 3.4 changelog entry

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## dev
 
+- **Feature: Support Ruby 3.4.0**
+
+  The agent now supports Ruby 3.4.0. We've made incremental changes throughout the preview stage to reach compatibility. This release includes an update to the Thread Profiler for compatibility with Ruby 3.4.0's new backtrace format. [Issue#2992](https://github.com/newrelic/newrelic-ruby-agent/issues/2992) [PR#2997](https://github.com/newrelic/newrelic-ruby-agent/pull/2997)
+
 - **Bugfix: Do not attempt to decorate logs with `nil` messages**
 
   The agent no longer attempts to add New Relic linking metadata to logs with `nil` messages. Thank you, [@arlando](https://github.com/arlando) for bringing this to our attention! [Issue#2985](https://github.com/newrelic/newrelic-ruby-agent/issues/2985) [PR#2986](https://github.com/newrelic/newrelic-ruby-agent/pull/2986)