Add changelog for 3.3.4-RC3

Author: WojciechMazur

changelogs/3.3.4-RC3.md

@@ -0,0 +1,13 @@
+# Reverted changes
+
+- Revert pattern matching improvements introducing regressions in 3.3.4 [#21573](https://github.com/scala/scala3/pull/21573)
+
+# Contributors
+
+Thank you to all the contributors who made this release possible 🎉
+
+According to `git shortlog -sn --no-merges 3.3.4-RC2..3.3.4-RC3` these are:
+
+```
+     4  Wojciech Mazur
+```