Add changelog for 3.7.1-RC2

Author: WojciechMazur

changelogs/3.7.1-RC2.md

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+# Backported chnages
+
+- Backport "chore: filter allowed source versions by import and by settings" to 3.7.1 (#23231)
+- Backport "Bump Scala CLI to v1.8.0 (was v1.7.1)" to 3.7.1 (#23230)
+- Backport "Mention extension in unused param warning" to 3.7.1 (#23229)
+- Backport "Revert recent changes to opaque type proxy generation" to 3.7.1 (#23228)
+- Backport "Remove premature caching of lookups for unused lint" to 3.7.1 (#23227)
+
+# Reverted changes
+
+- Revert "Make overload pruning based on result types less aggressive (#21744)" in 3.7.1-RC2 (#23239)
+
+# Contributors
+
+Thank you to all the contributors who made this release possible 🎉
+
+According to `git shortlog -sn --no-merges 3.7.1-RC1..3.7.1-RC2` these are:
+
+```
+     4  Hamza Remmal
+     4  Som Snytt
+     3  Jan Chyb
+     3  Wojciech Mazur
+     1  Piotr Chabelski
+```