Add changelog for 3.4.3

Author: WojciechMazur

Diff for: changelogs/3.4.3-RC1.md

@@ -6,7 +6,7 @@
 
 Thank you to all the contributors who made this release possible 🎉
 
-According to `git shortlog -sn --no-merges 3.4.2..3.4.3` these are:
+According to `git shortlog -sn --no-merges 3.4.2..3.4.3-RC1` these are:
 
 ```
     6  Wojciech Mazur

Diff for: changelogs/3.4.3.md

@@ -0,0 +1,13 @@
+# Highlights of the release
+
+- Revert "Approximate MatchTypes with lub of case bodies, if non-recursive" in 3.4.3 [#21268](https://github.com/scala/scala3/pull/21268)
+
+# Contributors
+
+Thank you to all the contributors who made this release possible 🎉
+
+According to `git shortlog -sn --no-merges 3.4.2..3.4.3` these are:
+
+```
+    8  Wojciech Mazur
+```