Add changelog for 3.2.1-RC4

Author: Kordyjan

changelogs/3.2.1-RC4.md

@@ -0,0 +1,14 @@
+# Backported fixes
+
+- Update Scala 2 library dependency to 2.13.10 [#16074](https://github.com/lampepfl/dotty/pull/16074)
+
+# Contributors
+
+Thank you to all the contributors who made this release possible 🎉
+
+According to `git shortlog -sn --no-merges 3.2.1-RC3..3.2.1-RC4` these are:
+
+```
+     2  Paweł Marks
+     1  Seth Tisue
+```