Add changelog for 3.4.0-RC4

Author: Kordyjan

changelogs/3.4.0-RC4.md

@@ -0,0 +1,14 @@
+# Backported fixes
+
+- Update jsoup dependency of Scaladoc to 7.2 [#19584](https://github.com/lampepfl/dotty/pull/19584)
+
+# Contributors
+
+Thank you to all the contributors who made this release possible 🎉
+
+According to `git shortlog -sn --no-merges 3.4.0-RC3..3.4.0-RC4` these are:
+
+```
+     2	Paweł Marks
+     1	Fabián Heredia Montiel
+```