Add changelog for 3.2.1-RC2

Author: Kordyjan

changelogs/3.2.1-RC2.md

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+# Backported fixes
+
+- Only look for synthetic applies under `TypeApply` with inferred arguments [#15970](https://github.com/lampepfl/dotty/pull/15970)
+- Improvements for implicit searches with top-level type variables [#16001](https://github.com/lampepfl/dotty/pull/16001)
+- Better types for class type parameters [#15951](https://github.com/lampepfl/dotty/pull/15951)
+- Avoid adding `NoSymbol` to gadt constraints in `TypeOps.instantiateToSubType` [#15965](https://github.com/lampepfl/dotty/pull/15965)
+
+# Contributors
+
+Thank you to all the contributors who made this release possible 🎉
+
+According to `git shortlog -sn --no-merges 3.2.1-RC1..3.2.1-RC2` these are:
+
+```
+     7  Martin Odersky
+     3  Kacper Korban
+     2  Paweł Marks
+```