Add changelog for 3.3.1-RC7

Author: Kordyjan

changelogs/3.3.1-RC7.md

@@ -0,0 +1,16 @@
+# Backported fixes
+
+- Tweak selection from self types [#18467](https://github.com/lampepfl/dotty/pull/18467)
+- Revert "Add reflect `defn.FunctionClass` overloads" [#18473](http://github.com/lampepfl/dotty/pull/18473)
+
+# Contributors
+
+Thank you to all the contributors who made this release possible 🎉
+
+According to `git shortlog -sn --no-merges 3.3.1-RC6..3.3.1-RC7` these are:
+
+```
+     3	Paweł Marks
+     1	Martin Odersky
+
+```