Add changelog for 3.3.4-RC4

Author: WojciechMazur

changelogs/3.3.4-RC4.md

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+# Reverted changes
+
+- Revert "Reduce projections of type aliases with class type prefixes" in LTS [#21609](https://github.com/scala/scala3/pull/21609)
+
+# Contributors
+
+Thank you to all the contributors who made this release possible 🎉
+
+According to `git shortlog -sn --no-merges 3.3.4-RC3..3.3.4-RC4` these are:
+
+```
+     4  Wojciech Mazur
+```