Add changelog for 3.3.1-RC3

Author: Kordyjan

changelogs/3.3.1-RC3.md

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+# Backported fixes
+
+- Add clause for protected visibility from package objects [#18134](https://github.com/lampepfl/dotty/pull/18134)
+
+# Contributors
+
+Thank you to all the contributors who made this release possible 🎉
+
+According to `git shortlog -sn --no-merges 3.3.1-RC2..3.3.1-RC3` these are:
+
+```
+     2 Paweł Marks
+     1 Martin Odersky
+
+```