Prefer encryption for the peer if the message is encrypted or signed with the known key (#3844)

Note that if the message is encrypted, we don't check whether it's signed with an attached key
currently, otherwise a massive refactoring of the code is needed because for encrypted messages a
signature is checked and discarded first now.

CHANGELOG.md

@@ -19,6 +19,7 @@
 - Fix cargo clippy and doc errors after Rust update to 1.66 #3850
 - Don't send GroupNameChanged message if the group name doesn't change in terms of
   improve_single_line_input() #3852
+- Prefer encryption for the peer if the message is encrypted or signed with the known key #3849
 
 
 ## 1.103.0